The party said last Sunday it would remove the two-term limit clause, setting the stage for Xi to stay in office indefinitely should he wish, prompting accusations from some in the country that China is set to become another North Korea.
While the party's official People's Daily said on Thursday the move did not mean life-long terms, the proposal has caused unease in China.
Parliament, which opens its two week-long annual session on Monday, will pass the amendment as the body is stacked with party loyalists who will not question decisions from the leadership.
Asked whether the constitutional amendment would mean Xi would stay in office for life, Zhang Yesui, a vice foreign minister and spokesman for parliament, did not offer a direct answer.
Instead he referred to the party constitution, which has no term limits for who heads the party and heads the military, positions Xi also holds and which are considered more senior in the country's hierarchy than the presidency.
The state constitution will therefore also mimic the party constitution in regard to the presidency, Zhang told a news conference.
The move "benefits protecting the authority of the party center and collective leadership with Comrade Xi Jinping at its core, and benefits the strengthening and perfecting of the national leadership system", he added, without elaborating.
The party gave Xi the title of "core" leader in 2016, a significant strengthening of his position at the time.
Xi will be formally elected to his second term as president at China's largely rubber stamp parliament. He began his second term as party boss in October.
State media has started ramping up the propaganda in favor of Xi in the run-up to parliament.
State television's WeChat account on Sunday began running an eight-minute long video entitled "The people's delegate Xi Jinping", showing pictures of Xi visiting ordinary people over a voice over of Xi talking about issues like poverty relief.
Xi is a member of parliament representing the northern region of Inner Mongolia.
(Reporting by Ben Blanchard; Editing by Muralikumar Anantharaman)