In the cascade hydropower stations composed of the leading reservoir， some daily regulated or unregulated hydropower stations， the leading reservoir may release a small flow of water for compensating operation besides normal generating flow according to the state of the intermediate inflow of downstream hydropower stations during the intervals between the dry season and flood season. This method can enhance the safety of the leading reservoir's flood control and reduce the discharge loss， providing more water for power generation to the downstream hydropower stations and improving the operating efficiency of the generator sets. A risk analyzing model for real-time compensating operation for cascade hydropower stations is developed in addition to a method for calculating the gain of real-time compensating operation. A risk quantifying approach to different compensation schemes for the leading reservoir is put forward， and a method for choosing the compensation scheme based on the maximum expected extra gain is recommended as well. The case study results show that the method is rational and effective for decision-making.