Abstract: According to the differences of soil water potential in the farmland, variable irrigation can save water as well as raise economic benefit. The decision support system for variable irrigation can forecast soil water content by using the forecast mathematical model of soil water content which is measured according to the different sampling sites using GIS. Irrigation or not can be decided by comparing the current soil water content with the light drought and serious drought indexes of the crops. The amount of irrigation can be decided by the analysis of economic benefit according to the model of water consumption-yield, thus the variable irrigation prescription and cluster analysis map can be made based on decision support system (DSS).