It is sending a crew of three, including the nation's first female astronaut, to the orbiting Tiangong space lab.
Their Shenzhou-9 capsule is set to lift off from the Jiuquan spaceport on the edge of the Gobi desert at 18:37 local time (10:37 GMT; 1137 BST).
A Long March 2F rocket will put the astronauts on a path to dock with Tiangong in a couple of days' time.
They will then spend over a week living and working in orbit before returning to Earth.
The mission is commanded by Jing Haipeng, who is making his second spaceflight after participating in the Shenzhou-7 outing in 2008 - the mission that included China's first spacewalk.
Jing's flight engineers are both first-timers.
Liu Yang will look after the medical experiments during the mission
China to see first woman in space
Liu Wang, a People's Liberation Army fighter pilot, has got his chance after spending 14 years in the China National Space Administration's astronaut corps.
Liu Yang will look after the medical experiments during the mission
China to see first woman in space
Liu Wang, a People's Liberation Army fighter pilot, has got his chance after spending 14 years in the China National Space Administration's astronaut corps.
Liu Yang, on the other hand, has emerged as China's first woman spacefarer after just two years of training.
Her role in the mission will be to run the medical experiments in orbit.
Shenzhou-9 follows on from the unmanned Shenzhou-8 venture last year that tested the technologies required to join a capsule to the Tiangong lab.
Those manoeuvres went very well and gave Chinese officials the confidence to send up humans.
When it arrives at Tiangong, the Shenzhou-9 craft is expected to make a fully automated docking, but there is a plan to try a manual docking later in the mission.
This would see the crew uncouple their vehicle from the lab, retreat to a defined distance and then command their ship to re-attach itself.
Liu Wang will take the lead in this activity. "We've done many simulations," he said during the pre-launch press conference.
"We've mastered the techniques and skills. China has first class technologies and astronauts, and therefore I'm confident we will fulfil the manual rendezvous."
