It is the country’s second aircraft carrier, after the Liaoning, and the first to be made domestically.
State media said the unnamed ship was “transferred from dry dock into the water” in the north east port of Dalian. Previous reports said it would be operational by 2020.
It comes amid heated rhetoric between the US and North Korea in recent days.
China has had only one operational aircraft carrier, the Liaoning, which it bought from Ukraine and refitted.
The new carrier will deploy Shenyang J-15 fighter jets, but is considered by many military observers to be technologically inferior to the 10 carriers used by the United States navy, says the BBC’s China correspondent Stephen McDonell.
The US has deployed warships and a submarine to the Korean peninsula, prompting an angry reaction from North Korea. China has urged for calm.
There is also the ongoing issue of competing territorial claims in the South China Sea.
The carrier is touted to be a significant upgrade from the Liaoning, which was built more than 25 years ago and is a refurbished Soviet ship bought from Ukraine. It has been seen by some analysts as a kind of training vessel in preparation for the new carrier, our correspondent says.
Chinese state news agency Xinhua said work had started on China’s latest aircraft carrier in 2013.
The launch was attended by the vice-president of China’s central military commission, Fan Changlong.
Officials smashed a bottle of champagne on the ship’s hull as “magnificent patriotic songs” played on loudspeakers and nearby ships sounded their horns in celebration, reported Xinhua.
The defence ministry said previously that it would carry China’s J-15 aircraft along with other planes, and that it would use conventional rather than nuclear propulsion.