The invention relates to a water intake reserved rock ridge water retaining cofferdam reinforcement system under a reservoir area operating water level. A reserved rock ridge water retaining cofferdamis reinforced through reinforcing systems such as steel pipe pile, consolidation grouting, membrane bag concrete, fiber glass reinforced concrete slabs inside the cofferdam, and inner-supported beams, scientific cofferdam reinforcement, consolidation and support systems are adopted, and the condition that dry land construction is created for water intake construction under reservoir operating water level is met. According to the water intake reserved rock ridge water retaining cofferdam reinforcement system under the reservoir area operating water level, the method is easy to operate, the cost is saved, the working period is shortened, and safety risk is lowered. The water intake reserved rock ridge water retaining cofferdam reinforcement system is suitable for situations of reservoir areas, near rivers, and poor geological conditions, and situation that pouring of underwater concrete cofferdam cannot be adopted.