An evaluation framework for joint operation of cascade hydropower stations was developed in this study. This framework is helpful to evaluate the operation performance of the cascade hydropower stations in order to improve the operation level. The power benefit of the cascade hydropower stations is chosen to be the evaluation object for multipurpose reservoirs and other targets are described as constraints according to the mandatory operation policy. The power generation is maximized by means of an optimal algorithm which is linked to a joint operation simulation model. This theoretical maximum power generation is introduced as an evaluative criterion to assess the indicated additional benefits compared with actual hydropower generation. In addition, an analysis module is involved to assess the influence of various factors on the operation performance. The developed framework was verified by the joint operation of the Three Gorges Project and Gezhouba cascade hydropower stations.