Speaking from the Great Hall of the People in Beijing on Friday, Xi touted the war to "resist US aggression and aid Korea" from 1950 to 1953 – the only military conflict between China and the United States – as a demonstration of China's military might against American imperialists.
Although fighting ended in a stalemate, the war established China as a major player on the world stage and Friday's commemorations closely fit with Xi's drive to promote patriotism and the unquestioned leadership of the ruling Communist Party.
"Seventy years ago, the imperialist invaders fired upon the doorstep of a new China," he said, AP reported.
"The Chinese people understood that you must use the language that invaders can understand – to fight war with war and to stop an invasion with force, earning peace and respect through victory. The Chinese people will not create trouble but nor are we afraid of them, and no matter the difficulties or challenges we face, our legs will not shake and our backs will not bend."
Xi stressed that "any country and any army, no matter how powerful they used to be" – a clear jab at the US – would see their actions "battered" if they stood against the international community.
"In today's world, the pursuit of unilateralism, protectionism and extreme egoism leads nowhere," Xi told the audience of government and party leaders, veterans and family members of those who served in what China calls the Chinese People's Volunteers.
"Arrogance, always doing as one pleases, acts of hegemony, overbearance or bullying will lead nowhere," Xi said, according to comments released by the official Xinhua News Agency.
The anniversary comes as China's relations with the US have sunk to their lowest level in decades as the sides feud over trade, human rights, allegations of spying and Chinese policies regarding Hong Kong, Taiwan and the South China Sea.
Beijing, meanwhile, remains North Korea's most important diplomatically and trading partner, and has pushed back at US efforts to bring economic pressure on Pyongyang to prompt it to end its nuclear weapons and missile programmes.
US relations with North Korea featured briefly in Thursday's presidential debate, with US President Donald Trump saying the Obama administration left him a "mess" to deal with in terms of tempering relations with North Korea.
Trump said he had warded off a war that could have threatened millions of lives, and that former President Barack Obama had told him he viewed potential danger from North Korean leader Kim Jong Un as among the greatest national security threats.
Democratic nominee Joe Biden said Trump had "legitimized" a "thug" by meeting and forging a relationship with Kim.
Trump countered that Kim "didn't like Obama" and insisted, "Having a good relationship with other countries is a good thing."