He also promised to lower import tariffs on consumer goods, especially cancer drugs, ease market access to the eldercare, healthcare, education and finance sectors, and completely open up the manufacturing sector to foreign investments.
He said there would be no victor in a trade war, and that both sides should remain rational and avoid giving in to emotions.
Li made no mention of a possible Chinese response in the event U.S. President Donald Trump raises import barriers over trade complaints against Beijing, but other officials say President Xi Jinping's government is ready to act.
"Any actions and tricks to split China are doomed to failure and will meet with the people's condemnation and the punishment of history", he said, to loud applause from the nearly 3,000 parliamentary delegates.
"We are unwilling to see a big trade deficit, not only with the U.S.", Li said. "We don't want to see a trade war".
Mr Li pledged to "strictly protect" intellectual property rights and ensure that no foreign firms will be forced to transfer technology to their Chinese partners as China opens its markets wider to foreign investors.
The US trade deficit with China ran to a record US$375 billion past year - but US exports to the country were also at a record.
Trump says Beijing has forced USA companies to transfer their intellectual property to China as a cost of doing business there, though China has insisted that technology transfers are not a condition of gaining market access.
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China argues that trade benefits both countries, but Li did acknowledge US concerns.
According to media reports, Mr Trump is set to announce this week a package of US$60 billion (S$79 billion) in annual tariffs on Chinese technology and consumer goods to punish China for intellectual property infringement.
"We should have the confidence in the future", he said.
Before the press conference, Li introduced China's four new vice premiers, including Liu He, widely regarded as China's new economic tsar.
On systemic financial risks being faced by China, Li said the fundamentals of the country's economy are "sound".
China aims to expand its economy by around 6.5 percent this year, the same target as in 2017, which it handily beat.
The Chinese central bank was being given responsibility for drafting important laws covering the banking and insurance sector, with regulation over the $42 trillion sector becoming more streamlined and tighter.
The formal visit would take place before or after the trilateral summit, where leaders are expected to discuss participation in China's Belt and Road Initiative to create a Eurasian economic zone, and exchange opinions on North Korea's nuclear and missile programs.