Speaking at the Great Hall of the People here on the 90th anniversary of the People's Liberation Army (PLA), Xi asked the military to always remain combat ready.
"We do not allow any individual, any organisation, any political party, at any time or by any means to split any single piece of Chinese territory," said Xi, who commands the world's largest standing army.
"No one can expect us to swallow consequences that damage our sovereignty, security and developmental interests," he said.
Xi said the PLA had done its duty to counter secessionist forces in Hong Kong and Macau.
The decades-old feud between India and China has a new addition: Doklam in the Sikkim section where both armies have been engaged in a stand-off.
Beijing wants New Delhi to withdraw troops from Doklam. New Delhi is for a simultaneous pullback of both Indian and Chinese troops.