This paper researches on sewage discharge condition along Tonghui River in Beijing. According to stationing principle and field investigation, there are 18 sewage outlets along Tonghui River and select 7 main water quality pollution indicators and sewage flow to assess the sewage outlets’ pollution distribution. By means of SPSS soft applied in principal component analysis method, paper analysis on the main pollution indicators and the main pollution contribution sewage outlets. The result shows 3 extracted principal components reflect 88.92% information of primitive variables. Then solve the formula of the 3 extracted principal components as F1, F2, F3. According to the contribution percentage of variance in table Ⅲ, the function of comprehensive evaluation expression can be deduced as F= 0.727F1+0.187F2+0.086F3. The results show that among the 18 sewage outlets, the worst pollution contribution is No.16 outlet, the 18 sewage outlets’ pollution contribution to Tonghui River is in the order of NO.16> NO.11> NO.12> NO.3> NO.8> NO.9> NO.13> NO.14> NO.17> NO.10> NO.15> NO.6> NO.18> NO.5> NO.1> NO.7> NO.4> NO.2. The assessment result is tally with the actual situation. Administrative means, technical means and management means are the effective measures to improve water quality of Tonghui River.