As more and more reservoirs are built, concentrated water releasing in the dry season will bring about additional flow compensation and the joint operation of cascade hydro plants is quite important. This paper discusses the water level decline strategy of four cascade hydro plants in the Jinsha River and analyses the relationship between guaranteed output and total power generation. Considering stochastic inflows, an implicit stochastic optimization method is employed and a multi-objective parallel differential evolution algorithm is proposed to extract dispatching rules. Finally, a method which combines discriminant method and dispatching rules is proposed for practical operations and achieves good performance. Compared with routine scheduling, the power generations of the proposed method are improved observably in different typical years. The average power generation increases about 3% with the same cascade minimum output.