Party congresses usually last 10 days. But details must first be approved by a meeting of the party’s Central Committee, which brings together hundreds of senior officials. The congress will elect a new Central Committee, which in turn will anoint the new leadership.

Mr. Xi is likely to present his new lineup publicly at the end of the congress.

The congress will select only party positions. The new government lineup will be appointed by a meeting of the legislature, called the National People’s Congress, which is likely to convene in March. Mr. Xi is then almost certain to be reappointed state president, and Li Keqiang appears likely to win another term as premier.

In the months leading up to the congress, Mr. Xi has shown a willingness to rework the rules of elite succession politics and to further consolidate his power. In July, for example, the party dismissed Sun Zhengcai, a fast-rising politician in Sichuan Province who had once been considered on track for a national post, and placed him under investigation.

Mr. Xi already holds more titles than many of his predecessors. He is general secretary of the Communist Party, chairman of the central military commission, and he is known as China’s “core” leader, a vague but powerful status that puts him on a pedestal with Mao Zedong, Deng Xiaoping and Jiang Zemin.

At the congress, Mr. Xi is likely to press to enshrine his ideology in the party’s constitution, helping to solidify his legacy, analysts say. News reports on Thursday hinted that Mr. Xi may get his wish. Xinhua, the official news agency, reported that the “spirit of General Secretary Xi Jinping’s series of important speeches” would be among the guiding ideas at the congress, alongside those of former leaders including Mao and Deng.

“That would be a fairly strong sign to the party that this is collective governance of one, and that all eyes should be looking to Xi Jinping,” said Jude Blanchette, a researcher at the Conference Board in Beijing who studies Chinese politics.

Still, Mr. Blanchette added, having more allies in crucial positions could leave Mr. Xi vulnerable to criticism if the Chinese economy underperforms or if a foreign policy crisis breaks out.

“The buck stops with him whether he wants it or not,” Mr. Blanchette said.