Considering the actual state of management in irrigated areas of our country, it is necessary to develop precision irrigation decision support system (DSS) of intelligence, which should be simple, convenient and easy to spread. This system adopts the optimization pattern based on genetic algorithm (GA) with two steps. The first step is to achieve the optimization of water allocation of the unitary crop in different growing periods. The second step is to achieve the optimization of water allocation of many kinds of crops. Moreover, combined with the expert system, it averts the limitations of genetic algorithm (GA) effectively when used to solve the problem of partial searching. This system adopts Maplnfo as the human-computer interface, which makes the decision visible and the system operational. In running structure, this decision support system (DSS) consists of five modules: the data acquisition module, the information management module, the simulate module of crop water allocation, the optimize module with genetic algorithm (GA) and the display module of irrigated areas information. The research, development, popularization, application of this system will supply scientific management and optimize allocation for our country's northern areas lack of water