To better remove the contamination on the surface of a heat-exchanger in urban sewage source heat pump system (USSHPS), this paper analyzes the feasibility of strong self-flushing on the basis of experiments and presents a new on-line self-flushing technique, which ahemately flushes part of heat transfer tubes, In addition, operation principles and the structure of the new heat-exchanger are introduced and the feasible economical and technological cleaning plans are given by design calculation and scheme comparison. The result showsthat keeping each tube washed for one minute with 5 m/s, the operating cost is lower than (￥)5 and when oneflushing pump alternately flushes 10-20 heat exchangers, the saved costs of flushing 10 tubes alternately are over 4 times of the increased costs.