A method for tracking a pollution source in process water is presented. Firstly, variation curves of drain water drained from different rinsing tanks are respectively obtained, and a water quality concentration of the drain water drained to a buffer tank is detected, so as to output a water quality variation curve. Then, an analytical comparison is performed on each drain water amount variation curve and the water quality variation curve within a same time interval, so as to output an analytical result of each flow of drain water in a range exceeding a predetermined water quality standard. In this manner, the drain water that exceeds the predetermined water quality standard can be tracked in real-time according to the analytical result, thereby quickly improving the process for discharging the drain water.