About 10 minutes into trading, the Dow Jones Industrial Average was up 1.7 percent to 24,377.31.
The broad-based S&P 500 gained 1.3 percent to 2,646.81, while the tech-rich Nasdaq Composite Index rose 1.3 percent to 7,041.92.
Xi, in a speech at the Boao Forum, pledged on Tuesday to lower tariffs on auto imports this year and take other steps to open the world's number two economy "wider and wider," addressing major complaints by the United States in an escalating trade row.
A series of tit-for-tat threats by the US and China to impose retaliatory tariffs on one another has rattled markets in recent weeks.
But Xi's remarks "has set a very positive tone for lowering US-China trade tensions," said Rajiv Biswas, Asia Pacific Chief Economist at IHS Markit.
"President Xi also pledged China's commitment to globalization as well as trade and investment liberalization."
Facebook rose 0.3 percent ahead of a congressional testimony by its chief executive Mark Zuckerberg over a consumer data scandal.
In his prepared statement, Zuckerberg took responsibility for security lapses at the world's largest social network.