Bathing wastewater contains a large amount of waste heat. A large temperature difference heat pump unit was proposed to maximize the recovery of heat energy from bathing wastewater by the authors. The rated design conditions of the unit are: the entry and exit temperatures of evaporator side bath wastewater are 30℃ and 6℃, respectively. The inlet temperature of tap water on the side of the condenser is 5℃, the outlet temperature of hot water is 45℃, and the theoretical calculation value of the maximum coefficient of heating performance (COP) is 4.9. In this paper, the effects of inlet temperature of tap water, outlet temperature of hot water and inlet temperature of bath wastewater on thermal performance of heat pump unit were studied experimentally. The experimental results show that the COP of the whole unit is 5.0 under the rated design conditions. When the inlet temperature of tap water increases from 5℃ to 15℃, the overall unit COP was reduced from 5.0 to 3.85. But if the inlet temperature of tap water is less than 10℃, the overall unit COP is higher than 4.5; When the temperature of the hot water outlet changes from 40℃ to 50℃, the overall unit COP gradually decreases from 5.3 to 4.9. And when the inlet temperature of bath waste water rises from 30℃ to 35℃, the overall unit COP rises from 4.8 to 4.95.