It is the country’s second aircraft carrier, after the Liaoning, and the first to be made domestically.
The as-yet unnamed ship was transferred into the water in the north-eastern port of Dalian, state media said. It will reportedly be operational by 2020.
It comes amid heated rhetoric between the US and North Korea and ongoing tensions in the South China Sea.
China has had only one operational aircraft carrier, the Liaoning, which it bought from Ukraine and refitted.
The US has deployed warships and a submarine to the Korean peninsula, prompting an angry reaction from North Korea. China has urged calm.