The 50,000 tonne new carrier was transferred from a dry dock into the water at a launch ceremony in northeast Dalian shipyard of the China Shipbuilding Industry Corp (CSIC), state-run Xinhua news agency reported.
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.
China began building its second carrier in November 2013. Dock construction started in March 2015.
The launch ceremony was attended by Fan Changlong, vice chairman of the Central Military Commission.
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The launch comes amid China's assertiveness in the South China Sea.
China claims almost all of the South China Sea, despite objections from the Philippines, Malaysia, Brunei and Vietnam. China has also created artificial islands in the area, outfitting some of them with military features.
The launch also comes amid heated rhetoric between the US and North Korea in recent days. The US has deployed warships and a submarine to the Korean peninsula, prompting an angry reaction from North Korea. China has urged for calm.
Recently state-run People's Daily quoted military experts as saying that the third aircraft carrier to be built in Shanghai may be nuclear powered
Earlier reports said Chinese navy which now has an expanded role among the military is set to raise its marine forces from 20,000 to one lakh as it started setting up logistic bases in Gwadar port in Pakistan and Djibouti in Africa.
China has enhanced the battle capabilities of its aircraft carrier Liaoning, with more than 10 pilots from carrier-based jet fighters and commanders getting their certificates, making China one of the few countries capable of training its own pilots for aircraft carriers.