Abstract: The water resources allocation of Western Chongqing region needs to be optimized because the insufficient self-yielded water resources and vulnerable water environment can't support the regional sustainable economic and social development. A water resource allocation model was established based on MIKE BASIN to simulate the main water supply projects, water users and rivers. Eco-environmental water demand of river control sections was calculated from three aspects: ecological basis flow demand, aquatic organism flow demand and self-purification flow demand. On the premise of returning ecological water occupied by domestic and industry and giving eco-environmental water demand the priority of water supply, a water resources allocation mode was put forward, in which domestic and industry water demand was met by pass-by water resources lifted from Yangtze River and Jialing River.