An eutrophication evaluation method of Gamma-Cloud model was proposed based on the theory of cloud model, with the assumption of asymmetry and unilateral constraint in membership distribution. Numeric characteristics of Gamma-Cloud model belonging to each eutrophication level were determined according to the established indicators; and the weight was calculated by analytic hierarchy process to generate Gamma-Cloud models of all indicators. Distribution of the certainty degrees belong to each level were determined after weight calculation; and the eutrophication level corresponding to the maximum certainty degree is the final evaluation. 12 lakes and reservoirs were evaluated with this model. Comparative researches with the methods of single index, variable fuzzy sets and normal cloud model shows that Gamma-Cloud model is effective and provides a new way of eutrophication evaluation.