Liu, along with Zhai Zhigang and Jing Haipeng, were chosen to be the main crew of Shenzhou 7, with Zhai as commander, on 17 September 2008. On 25 September, at 21:10 CST, they launched into space as China's third human spaceflight mission, and the first Chinese mission ever to have a three-man crew. Liu and Zhai participated in China's first-ever space walk.
Liu wore a Russian Orlan-M spacesuit, while Zhai wore the Chinese-made Feitian space suit. Liu remained in the open portal of the orbital module, assisting Zhai on his spacewalk; later in the space walk, Liu also performed a stand-up extra-vehicular activity, partially leaving the orbital module in order to hand Zhai a Chinese flag.