The new British prime minister will hold talks with US president Barack Obama on Sunday
Theresa May is heading to China for her first big entrance on to the international stage where she will hold one-to-one meetings with the world's most powerful leaders.
The G20 is also the first major summit since Britain decided to leave the European Union.
A Downing Street spokesperson said: "It is a real opportunity for the PM to send a clear message to the world's largest economies that Britain continues to play a bold, confident and outward looking role, as the UK leaves the EU."
Mrs May wants to show that the UK remains "open for business, that we will continue to be a strong and dependable partner".
She will make an intervention during a summit session to set out how she sees the UK's role and her desire for a "smooth and orderly departure from the EU and stronger trading relations in the future".
But the new British prime minister faces a row with her hosts over the Hinkley Point nuclear power station and is not expected to use the meeting to make an announcement on the project, which is backed by Beijing's state-owned nuclear firm.
Mrs May will have a meeting with President Xi Jinping on Monday, after the conclusion of the two-day summit in Hangzhou.
The prime minister will hold talks with US president Barack Obama on Sunday, and hopes to show that the UK remains a "dependable" diplomatic and trading partner in the wake of the vote to quit the EU.
Mrs May last met Mr Obama in April, when she was Home Secretary.
At that time the US leader warned that the UK would be at "the back of the queue" for a trade deal if it voted to leave the EU.
But amid reports that the planned US trade deal with the EU has stalled, the UK hopes for talks on a transatlantic agreement of its own with Washington.
During the summit, Mrs May will also hold her first face-to-face talks with Russian leader Vladimir Putin, and is expected to adopt an approach of "hard-headed engagement" especially on the issue of Russian bombings in Aleppo, Syria.
The Prime Minister will warn all members of the G20 that Islamic State militants who are being forced out of strongholds in Libya, are looking to find new safe havens in areas such as sub-Saharan Africa.
She will also have a meeting with her Indian counterpart Narendra Modi, with the trading relationship expected to dominate the agenda.