In the plain area, the water resources exchange closely. A unitive water resources system has been built up with the surface water and groundwater. Based on the criterion of the expenses and water supply, this paper studies the controlling model for conjunctive operation of surface water and groundwater,with which we can optimize the water resources with reasonable development, give a full play to the union regulation and control function of the reservoir between surface and underground reservoir, improve the using rate of the water resources, and achieve an optimal benefit of society, environment and economy.