The mission, which reportedly could last up to five days, is more ambitious and riskier than China's first manned space flight two years ago, which lasted just 21 1/2 hours.
The manned space program is a prestige project for the ruling Communist Party. The 2003 flight made China only the third nation, after Russia and the United States, able to send a human into orbit.
Ahead of the launch, China asserted on Tuesday that its aspirations in outer space are strictly peaceful, and that it opposes deploying any weapons there.
"The Chinese government has consistently advocated the peaceful use of outer space and opposed the weaponization of outer space," said Foreign Ministry spokesman Kong Quan at a regular news briefing.
"We do not wish to see any form of weapons in outer space, so we reaffirm that our space flight program is an important element of mankind's peaceful utilization of outer space."
A rocket carrying the Shenzhou VI capsule will blast off Wednesday from a launch site in the Gobi Desert of China's northwest, the official Xinhua News Agency said Tuesday.
It didn't give a time but said there would be a live TV broadcast from the Jiuquan Satellite Launch Center starting from between 8 to 9 a.m. (0000 to 0100 GMT).
Xinhua said a crew had been picked from a field of six finalists but didn't give their names.
A Chinese newspaper identified the pilot as Fei Junlong and said he would be accompanied by Nie Haisheng. The report by the Chongqing Morning Post didn't cite a source.
Nie was among three finalists for China's first manned space flight in 2003. He lost out to Col. Yang Liwei, who spent 21 1/2 hours in orbit before his capsule landed by parachute in China's northern grasslands.
The flight this week will be more complicated than the 2003 mission, according to state media.
Reports say the two astronauts will take off their 10-kilogram (22-pound) space suits to travel back and forth between the two halves of their vessel — a re-entry capsule and an orbiter that is to stay aloft after they land.
They will also conduct experiments, Xinhua said, but details have yet to be released.
The official China Daily newspaper on Tuesday dismissed rumors that plant seeds and animal semen would be carried in the capsule in order to study the effects of radiation. The paper said that because the capsule would be carrying human passengers, it would be insulated against radiation, making it impractical to conduct such experiments.
In a break with the space agency's typical secrecy, Xinhua said a live broadcast of the entire flight would be provided to foreign media.
Earlier reports said the liftoff and space flight would be shown on Chinese television with a brief delay, possibly to allow authorities to cut the signal if anything goes wrong.
None of the 2003 space flight was shown live by Chinese television.
Foreign reporters are barred from the remote launch base in the Gobi Desert in China's northwest. A handful of Chinese journalists are to be on hand for the liftoff, but have been warned that they might be ordered to hand over any photos or video — a possible image-control measure if anything goes wrong.
The Shenzhou — or Divine Vessel — capsule is based on Russia's three-seat Soyuz, though with extensive modifications.
Space suits, life-support systems and other equipment are based on technology purchased from Russia.
China has had a rocketry program since the 1950s and fired its first satellite into orbit in 1970. It regularly launches satellites for foreign clients aboard its giant Long March boosters.