"The whole army must strengthen its constitutional awareness, promote the constitutional spirit and be a loyal admirer, conscientious follower and staunch defender of the constitution," Xi told military officials on Monday.
China's rubber-stamp parliament on Sunday endorsed Xi's move to abolish rules limiting heads of state to 10 years in power.
The amendment also added the leader's eponymous political philosophy into the constitution: "Xi Jinping Thought on Socialism with Chinese Characteristics for a New Era."
It was the first constitutional amendment in 14 years and reversed the era of "collective leadership" and orderly succession that was promoted by late paramount leader Deng Xiaoping.
Xi, who is also head of the military, was speaking during a meeting of the People's Liberation Army and armed police at the ongoing annual session of the National People's Congress.
He sat at the head of a table dressed in a traditional Mao suit as officials diligently took notes.
Unlike most countries, China's armed forces are permanently under the control of the ruling Communist Party, rather than the state.
In his speech, he referred to the "revolutionary restructuring" of the military's organisational structure in recent years.
The changes have included the replacement of top military brass with Xi loyalists and the sacking of top generals for corruption.
Former chief of joint staff Fang Fenghui is facing prosecution for bribery, state media reports said in January. Former Central Military Commission vice-chairman Guo Boxiong was jailed for life in 2016.
Earlier this year, the party took control of China's paramilitary force, a move analysts said could have arisen from anxiety over the potential use of the police to stage a coup.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)