The invention discloses a surface water quality evaluation method based on combined weight, which includes the following steps, firstly selecting water quality indexes to build a water quality evaluation system, then adopting the subjective weighting method, the analytical hierarchy process, the objective weighting method and the super-standard weighted method to obtain three groups of weight vectors of the water quality indexes, and adopting the weight synthesis method based on the ideal point method for weight synthesis, so as to confirm the combined weight of the water quality indexes; taking the water quality indexes as evidences, calculating the basic trust distribution of the evidences to various water quality types, and then performing evidence synthesis based on the evidence additive synthesis rule of the combined weight; and selecting the water quality type with the highest trust degree as the water quality evaluation type as per the evidence synthesis result, and analyzing the variation trend of water quality as per the variation of trust degree of various water quality types. The surface water quality evaluation method provided by the invention integrates the influence of various water quality indexes to determine the water quality type, is objective and reasonable in evaluation results, and can be used for analyzing variation trend of water quality at the same time.