The deal resets some US tariffs on Chinese exports that have been in effect since September, and enables Beijing to avoid additional taxes on nearly $ 160 billion of the country's goods.
Yellen admitted that tensions eased after the US and China reached the "ceasefire". However, she reminded the Hong Kong audience that most Chinese goods are still subject to "fairly high" US tariffs. "We haven't seen any significant tariff cuts," she said.
Under the original agreement, tariffs of up to 25% will remain on China's $ 370 billion worth of goods. That is around two thirds of Chinese exports to the USA.
Yellen said that the first phase tariff reduction is not "very noticeable" for US households. And overseas companies wishing to do business in China continue to face uncertainty about supply chain and investment decisions. The former central banker also warned that "more problematic, more difficult" problems would arise.
Among other things, she mentioned subsidies for Chinese state-owned companies and the competition between the USA and China in relation to artificial intelligence, superfast 5G mobile radio networks and other technologies related to national security.
"These problems will be very difficult to solve and have major ramifications for the global economy," she said.
China and the United States are already fighting for the Chinese technology company Huawei, a leading global provider of telecommunications equipment for building 5G networks.
If the two economic superpowers fail to find a common denominator, the pace of technological progress could slow down and complicate the introduction of new commercial applications.
The world could even split into competing groups for technology, making trade difficult and global integration much more difficult.
"Technologies that have been developed in one place in the world must and can be used worldwide and form the basis for the further progress of technological innovation," she said.
"Losing these synergies" would be a very negative development. "I hope we won't go there," said Yellen.