Cheng began her career in the 1975 working on a number of Television Broadcasts Limited series. She also hosted the Hong Kong version of the game show The Weakest Link from 2001–2002. In 1980, she made her debut along with Chow Yun-fat. After her film debut her output became so prolific that at one point she was working on nine films simultaneously, leading her to have the nickname "Nine films Cheng." It was also during this very prolific time in her career that she became the highest paid actress in the region, beating out Maggie Cheung, Anita Mui and Michelle Yeoh, who rounded up the top 5.
Cheng began hosting entertainment programmes for TVB in 1997, she returned to acting with a critically acclaimed performance in the TVB sitcom, "War of Genders". It immediately become the highest rated show for the network TVB and garnered Cheng a Best Actress trophy at the annual awards.
Cheng is single. She is said to have held on to her personal philosophy of "no marriage and no kids".
Cheng's parents frequently quarrelled and even fought during her childhood. They eventually divorced. Cheng's father left, and her mother struggled to support Cheng and her younger brother. As a result, Cheng is said to be concerned about getting married and has said she does not want to have kids.