A PLA-backed video accuses the US and Britain of using Hong Kong as a base to destabilise and infiltrate mainland China.
The film, produced by the military's National Defence University and General Staff Department, as well as the Chinese Academy of Social Sciences, singles out four social movements it says are being manipulated by the two countries' missions in Hong Kong. One of them is the Occupy Central pro-democracy campaign.
A political analyst said the criticism was a significant step by Beijing to tighten control over Hong Kong.
Entitled Silent Contest, the 100-minute documentary explores China's struggle against "American hegemony". It says both the US and Britain have abnormally large consulates through which to infiltrate Hong Kong and nurture subversives.
Watch: A clip from China's People's Liberation Army documentary
"The US consulate in Hong Kong has some 500 staff, while the British one has about 400. Such large bodies of staff are very rare for foreign consulates," the video narrates in Putonghua.
"The [annual rallies on] June 4 and July 1, the movement against national education and Occupy Central … were all influenced by the US and British consulates.
"[The offices] not only interfere with Hong Kong's internal affairs, but become a base for anti-Chinese and anti-Communist powers."
The British consulate denied the allegations, saying it had "about 150 employees at its peak". The US consulate declined to comment.
The video was made under the supervision of two senior People's Liberation Army generals, Liu Yazhou and Wang Xibin , at the university, which is run by generals and where many teaching staff are mid-ranking PLA officers.
Veteran China analyst Johnny Lau Yui-siu said the rare attack reflected Beijing's worries about radical forces in Hong Kong.
"The PLA seldom takes on Hong Kong affairs," Lau said. "The heavy criticism shows Beijing's worries that Hong Kong's radical forces would be manipulated by foreign states."
Occupy organiser Dr Chan Kin-man said: "The accusations are not backed by any substantial evidence. This … smearing shows China's worries. I believe there will be more … to come."