Abstract: The optimal allocation of water resources for multi-purpose uses is a problem of multi-objective decisionmaking in a river basin. According to the characteristics of the Heihe Main River System and System analysis of water allocation and utilization,this paper introduces in detail the multi-objective planning model of water resources optimal allocation in the Heihe Main River System, Objectives of both aspects of national economic development and environmental quality are considered in the developed model. We design six water users of industry, agriculture, forestry, animal husbandry (irrigation pasture), ecological forest and grasslanda nd municipal, human and livestock drinking demands bised on subregion, and give the rations of surface water and ground water respectively. Through two sets of data calculation it has proved that the multi objective planning model of water resources optimal allocasion can provide a quantitative water allocation criterion in the rational development and utilization of water resources of the Heihe Main River System.