It doesn't seem to have hurt the prolific composer's career. His fourth opera, Poet Li Bai (he has written a number of other chamber operas) recently had its premiere in the US to rave reviews. The lavish production will have its premiere on the mainland next month as part of the Beijing Music Festival.

Guo has also written concertos for erhu and bamboo flute, as well as western orchestras, and a great deal of music based on folk melodies. Informing all his art is a mixture of urban savvy, gleaned from his Chongqing childhood, and the lyrical, earthy music of the Sichuanese countryside. Mostly, farmers sang about sex, he says.

'Even if it was the Cultural Revolution, 'the mountains were high and the emperor far away',' Guo says, quoting a well-known Chinese saying.

Touring the countryside from the ages of 14 to 21 with the Chongqing Song and Dance Troupe (he played on his violin such Cultural Revolution staples as The White-haired Girl and The Red Detachment of Women), Guo listened as farmers sang about love. 'Say they would sing about a cupboard where bowls were stacked one on top of each other. What they were really saying was that people are the same - on top of each other in bed,' he says, with a mischievous glint in his eye.

He delights in earthy metaphors. Such as when he explains how he dislikes talking about the cliche of east meets west. 'Sometimes, you can eat something and not digest it, and then you just s*** it out. Sorry, I'm a bit crude.'

Guo says he believes strongly in the individuality of the artist's voice. 'Take the symphony as an example. It began in Germany. Then went to France, where it had its practitioners. To England. Finland, and Sibelius. To Russia, and Tchaikovsky and Shostakovich. In America, it has its own style. And in China too - a Chinese style. You can't even talk about a Chinese style, but an individual's style. I think it's more important to talk about individual style.'

Guo is attached to the composition department at the Beijing-based Central Conservatory of Music, which he used to head. He has taken on an advisory role to allow him time to compose, but still teaches. A graduate of the conservatory, he was among the first intake of students after the Cultural Revolution in 1978.

Avant garde without being hard on the ear, Guo's musical style has won him a devoted following. And although he has stayed loyal to his roots, his audience is global.

'Whether in China, Europe or America, the audience's reactions are pretty much the same, so it doesn't matter to me where my operas are staged,' he says.

Guo's major operas have had their premieres overseas: in 1994, WolfCubVillage, based on author Lu Xun's Diary of a Madman, had its debut in Amsterdam at the Holland Festival, where critics hailed it as a 'masterpiece of madness'; Night Banquet (1998/2001), based on a painting about a Song dynasty court official, had its premiere in London and Hong Kong; a third opera, Fengyiting (2004), also had its premiere in Amsterdam, although chamber operas Mu Guiying (2003) and Hua Mulan (2004) made their debuts in Beijing's Capital Theatre, directed by Li Liuyi.

On a recent broiling Beijing afternoon, the thermometer inching towards 40 degrees Celsius, the stocky man with bottlebrush hair rolls a cigarette, the first of many. Speaking in a sonorous bass - helped, he says, by his smoking habit - he excuses his tobacco addiction as another legacy of Cultural Revolution mayhem.

'No one paid any attention to me during those years and so I smoked. Back in the 1970s, no one ever said, don't smoke.' His trademark pipe has been shelved for the season. 'It's just too hot to hold the bowl on a day like this.'

Perhaps because his beloved pipe is gone, Guo fiddles constantly - with a receipt on the table or a business card, rolling it up repeatedly until it's shedding fibres.

A composer must write every day, he says. That explains why he wrote so much film music during the 1980s and 90s, when other commissions were thin on the ground. Key scores include Jiang Wen's In the Heat of the Sun (1994) and Zhang Yimou's Riding Alone for Thousands of Miles (2005). But those days are over. 'I find it unsatisfying. It's really different from writing your own music because you have to listen to the director. You have no control. Zhang would tell me what to do all the time. He couldn't write music himself, or he would have. There's no freedom in writing music for films. No, that's a door I've closed.'

Guo's musical style pays homage to all the shibboleths of post-Schoenberg composition, such as atonality and disharmony, but he says Poet Li Bai represents a new direction. 'I've never pandered to the audience's taste, but I have to say that with Li Bai, I've come 360 degrees. Li Bai is much more lyrical. It's much harder to write music you think other people will like. It's easy to write music that's pure and self-expressive. These days, for a composer to write harmonious music, that takes courage.'

The opera, which was performed for only one night, has attracted much attention from the press, with the New Beijing News labelling him a genius. Guo, the child of farmers who joined the Communist armies in the 1930s and who 'had nothing to do with art', dismisses the praise.

'I'm very confident, but I'm not arrogant. But I lose my temper easily with people who aren't serious about their work. In an orchestra, not every player is going to enjoy every piece of music they play.

'But you have to be professional and have a serious attitude. What I hate most is when people aren't serious about their work. Some people think that makes me arrogant. But what I'm asking for is very basic.'

10th Beijing Music Festival, Sept 21-Oct 26; Poet Li Bai, Oct 9, 7.30pm, Poly Theatre