China on Sunday held a massive parade, involving 12,000 service personnel and about 700 aircraft and pieces of ground equipment, at the expansive Zhurihe training base in China's Inner Mongolia Autonomous region.
President Xi, who presided over the military procession, stressed the need to build a "world-class" army capable of "defeating all invading enemies."
"The world is not all at peace, and peace must be safeguarded," said Xi, wearing a camouflage military suit, during a speech.
"Today, we are closer than ever before to the goal of the great rejuvenation of the Chinese nation, and - more than any other time in history - we need to build a strong people's military," he said.
It was the first time that China marked its Army Day with a military parade since the 1949 revolution and also the first time Xi observed a parade of this size in the field, according to the official Xinhua news agency.
The PLA, originally called the Chinese Workers' and Peasants' Red Army, was founded in 1927 and is the world's largest standing military.
China is in a territorial dispute with India and with some of its other neighbors in the East and South China Sea. While strengthening its military, the country has been seeking a peaceful rise to a global power status.