In order to optimize the investment and operating benelits, the cost present value method and MATLAB software were used for mathematical calculations to compare and select the pipe diameters for a drainage pipeline project in a new pumping station. The results showed that if the pumping station operated for 30 years with water flow rates of 30000, 45000, and 60000 m3/d, pipeline with nominal diameter of 800 mm was more economical and can effectively deal with the project investment benefitproblem caused by the uncertainty of sewage flow rate.