Through applying PPE model based on RAGA in the investment decision-making of water saving irrigation project, this study turns multi-dimension data into low dimension space. So the optimum projection direction can stand for the best influence to the collectivity. Thus, the value of projection function can evaluate each item good or not. The PPE model can avoid jamming of weight matrix in the method of fuzzy synthesize judgement, and obtain better result. The authors want to provide a new method and thought for readers who engaged in investment decision-making of water saving irrigation and other relative study. [Nature and Science 2003;1(1):57-61].