The move helps to elevate him to levels of authority close to those of Mao Zedong and Deng Xiaoping.
The theory is likely to be incorporated into the constitution of the ruling Communist Party later this month.
The world's second largest economy has taken steps to rein in debt and cool the housing market.
The US would "never have the same relationship with China, a non-democratic society," he added.
A ban on the import of waste in China is about create a major blockage backing up through the global waste disposal system
Getting views on Kim Jong-un proved quite a challenge for our correspondent at the Communist Party Congress.
Xi Jinping's grand speech even had members of his own party checking their watches.
The president tells the Communist Party congress it is time for China to "take centre stage".
The gathering determines who leads China and the country's direction for the next five years.
Health risks and job losses are among the harms many in China face in the push for economic change.