The "volunteers" from "all walks of life" have been trained and will be sent to "every street, every alley" as well as stores and markets, the official Xinhua news agency said late Wednesday, citing a Beijing police spokesman.
They will look for signs of "security hazards" and report them to police, it added.
The Chinese government often uses huge amounts of manpower to strengthen security during major events, such as the 2008 Beijing Olympics and the following year's 60th anniversary of the founding of Communist China in 1949.
A series of other measures have also been taken for the parade on September 3, which will mark the 70th anniversary of victory over Japanese forces as well as the broader defeat of the Axis powers in World War II.
Communist China generally shies away from the vast annual demonstrations of military might that were a hallmark of the Soviet Union, normally holding such events once a decade to mark the foundation of the People's Republic.
But Beijing is becoming increasingly assertive in the region and regularly accuses Tokyo of failing to show sufficient contrition for Japan's 20th-century invasion of China.
Other than Russia's Vladimir Putin few major foreign leaders have said they will join, although South Korean officials said Thursday that President Park Geun-Hye would attend the broader commemorations - but no final decision has been made on whether she will attend the showpiece parade.