To improve the management of irrigation district is a key to develop water-saving agriculture. Based on the basic principles of water-saving irrigation, and using the method of Modified Penman Monteith and water balance equation, The system of irrigation management and decision support based on WEBGIS was developed, which is according to the soil moisture, crop growth status, meteorology change and the physiological and ecological index of crop that is monitored, and the situation of water supply and crop water-saving irrigation system were also combined with the system. With the help of the GIS, the system under discussion can predict the water requirement of the irrigation district so as to optimize the allocation of the water resources, to provide a decision support for irrigation managers, and to finally realize desirable irrigation practice. Besides, it will promote the automation, informationization, and intelligent of the irrigation district management.