In the light of the demand of water level decision in period end of scheduling of medium and long term power generation planning of hydropower station group, the paper established the joint optimal dispatching model which took the maximum power generation capacity as the target,and used improved combination dynamic programming algorithm of discrete differential and successive approximation to solve the model.It took the hydropower station group of Wujiang and Beipanjiang basin in Guizhou province for example,and using the actual inflow process in 2013, this model is compared with optimization objective of maximum power generation and compensation benefit. The result shows that the model can automatically determine the scheduling strategy of reservoir according to the change of power generation efficiency of power station,and relized the synchronization optimization of water level decision of hydropower station group dispatching and corresponding generation planning . The model can accurately reflect the dynamic game relationship of total generating capacity in scheduling period and total energy storage at the end of scheduling period.