The merits of the sewage source heat pump system are remarkable on energy efficiency and pollution reduction. Based on the fouling resistance law, the test bench was established on growth characteristics of fouling in copper pipe. The experiment has been carried on and the growth characteristics of fouling in copper pipe were obtained with the asymptotic agglomeration forecast model. It is found that the fouling induction period of the sewage is 21 hours in the smooth copper pipe, the fouling resistance settling time is 95 hours, and the stable fouling resistance is for 1.5×10-5m2K/W.