In view of such key problems in the medium and long term power dispatch as the electricity quantities with differences， power grid safe operation conditions， and by improving the Benders decomposition applied in the unit commitment problem， a two-stage medium and long term power dispatch model based on electricity quantities with differences is proposed considering both the solving efficiency and optimized characteristics. The gradual process of coordinated parameter correction is presented to match the master and slave problem so as to obtain the optimized solution for the original problem. Based on an actual application case of electricity quantities with differences in a regional power system in China to realize energy saving power dispatch， the feasibility and solving efficiency of the two-stage model proposed is demonstrated through simulations of medium and long term power dispatch.