Abstract: To solve the problem of the defective rationalization in urban water supply distribution,a water allocation model optimization arithmetic based on particles swarm optimization( PSO) was proposed. The arithmetic took surface water,ground water,tap water and reclaimed water as water supply,and contained four water-using,e. g. life,industry,agriculture and environment. A model of considering the cost of water exploitation was built. The water allocation model was constructed PSO and the optimal allocation scheme was proposed. Through the case study,the feasibility of the proposed method was proved. The arithmetic provides reference and support for water resource allocations in the future.