They allegedly planned to divorce their respective spouses and get married after they had accumulated enough money to maintain their lives together.
Li Ping was also found guilty of smuggling though details of the charge were not given.
Cheng has appealed but if the sentence is carried out, he will be the most senior official to be executed for bribery since the Communist Party came to power in 1949.
Conspiracy
The Chinese press has detailed how the two lovers conspired to abuse Cheng's power in the poor southern region of Guangxi between 1992 and 1998.
State media said Li acted as an lure for Cheng to attract bribes, including diamond rings and expensive watches, in return for selling state land cheaply, granting development contracts and promoting colleagues.
Coastal Guangxi is notorious for piracy and smuggling.
The pair was caught on video gambling heavily in casinos.
They allegedly planned to divorce their respective spouses and get married after they had accumulated enough money to maintain their lives together.
Li is reported to have met Cheng in 1992 when working at a hotel owned by the Guangxi government and became his lover soon after.
War against corruption
Li and Cheng's sentences are seen as a warning that the government is serious about its fight against corruption.
President Jiang Zemin has announced a full-scale war against corruption in the Communist Party.
Thousands of officials accused of abuses have been fired, fined, imprisoned, expelled from the party and in some cases executed.
In Guangxi alone, there has already been one execution and a number of arrests.
A vice-chairman of the provincial government, Li Chenglong, was convicted and executed in April for corruption.
Xu Bingsong, also a vice-chairman of the provincial government, was given a life sentence last summer for his role in a $66,000 corruption scandal.