Astronauts Nie Haisheng, 56, Liu Boming, 54, and Tang Hongbo, 45 will, among other things, work on testing the station's technical equipment.
The assignment is one of several that aims to complete the station.
Since 2003, China has sent a total of 11 astronauts into space, but this is the first time they have a crew that stays for 90 days.
The space station is one of many Chinese projects in space.
Probes have previously been landed on Mars and the moon.
The space station will give China a permanent presence in space when completed.
The country does not have access to the larger International Space Station ISS, as the US space agency Nasa is banned from cooperating with China.
See how the astronauts dock in the station in the video above.
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