Abstract: Along with the emergence of joint operation situations in a cascade reservoir system, the current assessment method of reservoir power generation is unable to meet the needs of economic operation, and the assessment of jointly-operated complex systems is more difficult. To overcome the limitations of traditional methods, this paper presents a method of potential optimization assessment that uses an optimal operation model to calculate the power output and its completion rate for cascade reservoirs, and considers model constraints by the main factors of power output. Combing this method with traditional assessment, we have achieved a comprehensive assessment of cascade reservoirs, i.e. assessing the existing situation and guiding the future operation. In a case study of the Wu River cascade system, its current comprehensive operation level is assessed by a traditional method and our new method. The results show that this system has excellent operation levels and the major factors of its power generation are runoff, runoff forecasting, and power network stability. The assessment results are comprehensive and objective and provide a technical support to the Wu River cascade in operation level improvement, water-saving, and power output growth in the future.