Positive and negative ideal solution created by traditional TOPSIS evaluation method is easy to cause reversal problem and the used Euclidean distance can not consider the correlation between decisionmaking indicators.For such problems，this paper proposes an improved TOPSIS method based on weighted Mahalanohis distance.The first is using the maximum difference dormalization method to eliminate the reversal problem in the traditional TOPSIS method，and the second is using the orthogonal transformation method by using the evaluation scheme after the transformation to calculate Mahalanohis distance to positive and negative ideal solution to replace the traditional Euclidean distance.The case analysis proves that the improved TOPSIS method is superior to the traditional method.