Xi, speaking on a rostrum overlooking Beijing's Tiananmen Square before the parade began, said China would cut by 13 percent one of the world's biggest militaries, currently 2.3-million strong.
He gave no time frame for the reduction, Reuters reported. Chinese Troop numbers have been cut three times already since the 1980s.
"Prejudice and discrimination, hatred and war can only cause disaster and pain," Xi said. "China will always uphold the path of peaceful development."
He then descended to Beijing's main thoroughfare and inspected rows of troops, riding past them in a black limousine and bellowing repeatedly: "Hello comrades, hard-working comrades!"
More than 12,000 soldiers, mostly Chinese but with contingents from Russia and elsewhere, then marched down Changan Avenue, led by veterans of World War Two carried in vehicles.
They were followed by ballistic missiles, tanks and armored vehicles, many never seen in public before. Advanced fighter jets and bombers flew overhead in a highly-choreographed spectacle that lasted around 90 minutes.
Among the weapons China unveiled for the first time was an anti-ship ballistic missile, the Dongfeng-21D, which is reportedly capable of destroying an aircraft carrier with one hit.
Also shown were several intercontinental ballistic missiles such as the DF-5B and the DF-31A as well as the DF-26 intermediate range ballistic missile, dubbed the "Guam killer" in reference to a US Pacific Ocean base.