Between 1991 and 1992, he was hired as a full-time member of the Central Policy Unit, a think tank of the Hong Kong government.

He joined the City University of Hong Kong as a chair professor of the Political Science and Coordinator of the Contemporary China Research Project in July 1992.

[4] Cheng was a commentator on political affairs and in the early 1980s witnessed the Sino-British negotiations over Hong Kong's sovereignty.

[1] He was the convenor of the Power for Democracy, a pro-democratic organisation set up in 2002 to co-ordinate the pan-democracy camp in the elections to avoid candidacy clashes.

The proposal was not accepted as the National People's Congress Standing Committee (NPCSC) set limits on the electoral method in its decision on 31 August.