In its readout of the call, the Chinese state media said Mr. Trump had "stressed that he fully understood the great importance for the USA government to respect the One China policy", and that "the US government adheres to the One China policy".
President Donald Trump and Chinese President Xi Jinping spoke by phone on Thursday evening for the first time since Trump's January 20 inauguration, marking a significant de-escalation in the White House's aggressive posture towards the world's second-largest economy.
Chinese state-run newspaper The Global Times called Trump "as ignorant as a child in terms of foreign policy" for his remarks, and the Chinese government persisted that the one-China policy is "the political foundation of China-U.S. relations" and non-negotiable.
He later threw doubt on the "One China" policy, suggesting that it was up for negotiation and could form part of talks on trade, drawing rebukes from official Chinese media.
Foreign Ministry spokesman Lu Kang said China "highly commended" Trump for the letter to Xi.
Abe and Trump are set to discuss trade and the Japan-U.S. Security Treaty.
Bonnie Glaser, the director of the China power project at the Center for Strategic and International Studies (CSIS) think tank in Washington, said the conversation between the two leaders, which had taken nearly three weeks to arrange, would calm fears that US-China relations were on the verge of a damaging breakdown.
Trump Moves to Gut Financial Regulation, Rule Intended to Protect Retirees
The Trump administration has argued Dodd-Frank has not achieved its objective and is an example of government over-reach. It will not take effect immediately and awaits Senate confirmation of Trump's Treasury Secretary nominee Steve Mnuchin.
After winning the election past year, Trump angered Beijing as he posted a tweet that seemed to question the one-China policy and he received a phone call from Taiwan leader Tsai Ing-wen.
Flynn and his deputy, K.T. McFarland, then personally delivered Trump's letter to China's ambassador to the U.S., Cui Tiankai. The US cut formal ties with Taiwan in 1979.
"President Trump stated that he looks forward to working with President Xi to develop a constructive relationship that benefits both the United States and China", it said.
Earlier Thursday, Trump sent a letter to Xi that thanked him for his congratulatory message after Trump's swearing-in last month.
Mr Trump placed the long-standing policy in doubt when he spoke with Taiwan's president in December.
It is also noteworthy that Chinese direct investment accumulated in the United States economy since 2000 exceeds 100 billion dollars, and that exchanges between peoples between both nations have continued to strengthen, so there is no reason to bet on a constructive bilateral relationship. "Trump has stopped openly challenging China's core interests, and instead showed respect to Beijing", the paper said.