Project investment decision-making system is a typical grey system which has the characteristics of some information uncertainty. This thesis tries to combine organically grey system theory with AHP. It computes judgement matrix and builds model through weighted grey relevancy degree, which provide an efficient decision making pathway. Grey relevancy analysis method is used to handle with power project investment decision making process. Then the multi-objects are weighted through AHP method. Finally, weighted grey relevancy degree is computed to select the optimal investment plan from alternatives which leads decision making result is more scientific.