Yang is to stay with the company at a high level but is being replaced in the hot seat by long-standing employee Li Fanrong, CNOOC announced on Wednesday.
The Chinese oil giant said Yang was stepping aside "due to his responsibility as the president of China National Offshore Oil Corporation which requires more of his time".
As a result, Yang will move from being an executive director to a non-executive director on the board but stays on as vice chairman to concentrate on company strategy.
With effect from Wednesday, Yang has been replaced by Li who has been with CNOOC group for over 20 years. The China and UK-educated qualified senior engineer has been president of CNOOC since mid September last year.
A veteran of the Chinese oil and gas industry with over 27 years experience, Li joined CNOOC in 1984, filling numerous roles before becoming vice president in May last year.
On the changes at the top, chairman Wang Yilin commented: "On behalf of the board of directors, I would like to welcome Mr Li on his appointment as new chief executive officer of the company. I would also like to express our appreciation and gratitude to Mr Yang for his outstanding contribution to the company.
(upstreamonline.com, Edited by Topco)