The Strategic Investment Agreement (SIA) was signed in the presence of Chinese President Xi Jinping and the Prime Minister David Cameron.
Work to build the £18bn nuclear plant is due to get underway in the coming weeks.
Hinkley Point C's Two European Pressurised Reactor's (EPR) are to provide reliable, low carbon electricity to meet roughly 7% of the UK's electricity demand.
The project has achieved planning consent, design approval for the EPR reactor and a nuclear site licence.
Under the SIA, EDF's share in Hinkley Point C will be 66.5% and CGN's will be 33.5%.
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CGN is to make its investment through its new company called General Nuclear International (GNI).
EDF and CGN have also agreed the Heads of Terms of a wider UK partnership for the joint development of new nuclear power stations at Sizewell in Suffolk and Bradwell in Essex.
EDF Chairman Jean-Bernard Lévy said: "I am confident that our experience and ability mean we will successfully deliver Hinkley Point C and subsequent projects.
"We are planning for a final investment decision within weeks so that we can move forward with construction."
He Yu, Chairman of CGN, said: "Entering the UK's nuclear market marks a new phase for CGN. At the same time this is also a triple-win for the existing nuclear energy partnership between China, France and the UK. CGN is highly committed to delivering safe, cost efficient, and sustainable energy and to supporting the UK's goal of becoming a low-carbon society."
Energy Secretary Amber Rudd added: "The UK is open for business and this is a good deal for everyone – Hinkley Point C will continue to meet our robust safety regulations and will power nearly six million households with low-carbon energy, creating over 25,000 jobs and more financial security for working people and their families. The Government will support new nuclear power stations as we move to a low-carbon future."
(LM/MH)
