The project was given the go-ahead, after China warned that “mutual trust” was needed between the countries.
Mr Ma is meeting Chancellor Philip Hammond to discuss investing in the UK.
Speaking before the eighth UK-China Economic and Financial Dialogue got under way, Mrs May said: “I’m determined that as we leave the European Union, we build a truly global Britain that is open for business.”
As we take the next step in this golden era of relations between the UK and China, I am excited about the opportunities for expanding trade and investment between our two countries.”
There will be an announcement that the Chinese contractor CITIC Construction is to invest £200m in the first phase of the £1.7bn London Royal Albert Docks project, headed by the Chinese developer ABP.
Philip Hammond promises ‘constructive’ US talks
And the UK will in turn invest up to £40m in the Asian Infrastructure Investment Bank based in Beijing, for a fund to help developing countries to prepare infrastructure programmes.
Mr Hammond, who is hosting the Chinese delegation at London’s Lancaster House, said: “The mutual benefits are clear. China is the world’s second-largest economy. UK exports to China have grown rapidly and Britain is home to more Chinese investment than any other European country.”
US President-elect Donald Trump has said he wants to apply 45% tariff barriers to Chinese imports in an effort to protect free trade.
Mr Hammond told the BBC: “Britain’s always believed that the best way long-term to protect and promote prosperity is free markets and free trade.”
President Trump has just been elected by the American people. He will want to consult with his advisers, talk to officials and I’m sure we will have a very constructive dialogue, as we do with the Chinese, with the new American administration.”
He added: “It’s about getting the right balance in the global trading system, so that we can have the benefits of open markets, while being properly and appropriately protected.”
One of Mrs May’s first acts on becoming prime minister during the summer was to order a review of the project to build Hinkley Point C, in Somerset, part-financed by China.
Writing in the Financial Times in August, Liu Xiaoming, China’s ambassador to the UK, said: “If Britain’s openness is a condition for bilateral co-operation, then mutual trust is the very foundation on which this is built.”
Right now, the China-UK relationship is at a crucial historical juncture. Mutual trust should be treasured even more.”
The UK government approved Hinkley Point C in September, saying it had imposed “significant new safeguards” to protect national security.