In this paper, an attempt has been made to apply an efficient technique, in order to solve the uncertainty of multi-objective optimization, in the field of sewage treatment plant. The traditional grey relational analysis has been extended to deal with the multi-objective optimization problems. The difficulty of traditional grey relational analysis exists in calculation of the multiple indicators and ignorance of the relationship among evaluating indicators. But there is no specific guideline for assigning these indicator weights. In this context, the present study aims to apply the entropy measurement technique in order to determine the weights of evaluating indicators, which avoids the subjectivity in the process of estimating the weights. The proposed method involves four steps, including 1) original data processing, 2) grey relational coefficients calculation, 3) indicator weight calculation, and 4) grey relation grade calculations. The previously mentioned method has been applied to optimize schemes of a sewage treatment plant. The paper demonstrates a detailed methodology of the proposed technique as well as its effectiveness and applicability.