At least 10,000 people participated in the drills, which involved 48 warships and 76 combat aircraft, the ministry said.
China's only aircraft carrier, Liaoning, participated in the parade with an exhibition of J-15 fighter jets under the observation of Xi.
The South China Sea has long been a hot spot in Asia. The Chinese government claims a large swath of territory across the sea, overlaid with claims from the Philippines and Vietnam, among others.
The massive exercises of the PLA Navy in the South China Sea sent a clear signal to the other plaintiffs in the region, as well as in the United States, Collin Koh, researcher of the Maritime Safety Program of the School of Studies Internationals of S. Rajaratnam, told CNN. "The PLA Navy is there and they are there to stay," he said.
Experts told CNN at the time that the large number of ships on display was a "demonstration of strength" by Beijing in the politically sensitive region.
At a press conference in March, the Ministry of Defense refused to confirm or deny the simulations or the ships that would be involved.
In a harbinger of future exercises, the provincial maritime authority of Fujian on Thursday announced naval exercises with real fire for April 18 in the Taiwan Strait.
The Chinese exercises are taking place amid growing tensions between Beijing and Washington over trade, but analysts have also waited for the Trump administration to tighten its policy on the South China Sea.
The US Navy UU He recently conducted several "freedom of navigation" operations with warships sailing near the increasingly militarized Chinese man made islands in the South China Sea, unleashing heavy protests from Beijing.
The forum is the Chinese equivalent of the World Economic Forum held in Davos, Switzerland, involving high-level talks between economic leaders.
Carrying out such large exercises directly in the back of their economic forum sent a clear message to the world, Koh said.
"This is to highlight that China is not only an economic power, but also a military and maritime power," he said.