The contradiction between the supply and demand of water resources becomes increasingly acute, so it is particularly important to optimize the allocation and efficiently utilize the limited water resources in the region. Water resources allocation in Hengshui city was taken as a case study. The demand of optimal allocation of Hengshui city water resources was considered comprehensively. The multi-objective optimal allocation of water resources model was established by taking the social benefit, economic benefit and ecological benefit as the objective function. The scheme of optimal allocation of water resources based on MOEA/D algorithm was given, and comparison experiments between the proposed scheme and the scheme based on NSGA-Ⅲ algorithm was done. The experimental results show that proposed scheme is superior to the scheme reported by literature, which can provide relevant support for the rational allocation of water resources in Hengshui city.