"The depth of our relationship means we can have frank discussions on all issues", she said earlier this week.
Mrs May, who visited China past year for a G20 summit, will be accompanied by her husband Philip and the leaders of 50 British businesses and commercial organisations.
Her trip comes as the House of Lords, the upper chamber of the British parliament, is scrutinizing a key piece of Brexit legislation and ministers sought to downplay a leaked government report offering only economic downsides to leaving the European Union in March 2019.
Ahead of British Prime Minister Theresa May's Visit to China, the British Ambassador to China Barbara Woodward briefed Chinese media on January 29, 2018 at her residence, saying a post-Brexit Britain would be able to "move a bit faster towards" deepening cooperation with China as well as jointly expanding Sino-UK commercial partnerships into third countries along the burgeoning Belt and Road.
"For a global trading nation like the United Kingdom it is doubly important, which is why I'm travelling to China at a crucial moment in the history of both our countries".
May travelled with her husband, Philip May, along with a delegation of 50 businesses and organisations, which her office said was "the largest" Britain has ever taken overseas.
In response to questions over how a "Global U.K." can link with the Belt and Road Initiative, the Ambassador said: "We would like to collaborate on practical projects, whereby now Chinese companies are working on over 90 percent of projects but there are British companies very keen to develop their partnerships which already exist with Chinese companies and take them into the third countries along the Belt and Road".
"It's natural that Belt and Road cooperation is an opportunity for the two sides to tap into our cooperation for win-win results", Chinese foreign ministry spokeswoman Hua Chunying told reporters on Tuesday. She will also visit the financial hub of Shanghai before heading home on Friday.
The British government, however, has been less sanguine about the project, with May's spokesman saying that while the idea holds promise, it is "vital that BRI projects meet worldwide standards".
Lord Patten, the last British governor of Hong Kong, has urged Mrs May to use the visit to privately raise what he says has been the steady erosion of freedoms and rights in the former British colony in recent years.
But business is the focus of her trip.
China is key to British hopes of forging new trade deals and partnerships around the world after it leaves the EU.