Abstract: A bench scale seawater source heat pump was developed, which consisting of a piston compressor and three plate heat exchangers (namely pre-heater, evaporator and condenser). The experiments were carried out on culturing water heating by the heat pump using wastewater as heat source in a lab flatfish culturing system. The performance, water heating and waste heat recovery effects of the heat pump were studied at different temperatures and flow rates of the heat source. The heating costs of culturing water by seawater source heat pump, coal (oil, gas) -fired boilers and electricity heating, etc were compared and analyzed as well. The results showed that it could obviously improve the performance of the heat pump by increasing the temperature and flow rate of the wastewater. When the temperature of wastewater was 8.0~9.0℃ and the flow rate was kept at 200~700 L/h, the coefficient of performance (COP) of seawater source heat pump was 2.61~3.85; while with wastewater temperature of 10.5~14.6℃ and flow rate of 200~700 L/h, the COP value of the heat pump reached to 3.19~5.12. Additionally, the water heating and waste heat recovery effects of the heat pump were closely related to the temperature and flow rate of wastewater. With relatively higher temperature and lower flow rate of wastewater as the heat source, the temperature increment of culturing water from the heat pump would increase correspondingly. Concerning the desirable water temperature (10~15℃) for flatfish culturing, the temperature of culturing water from the heat pump could rise from 7℃ to 10.0~12.8℃ if the temperature of wastewater was below 10℃ and the flow rate was under 400 L/h. Comparatively, the temperature of culturing water from the heat pump could reach to 10.4~13.4℃ by employing wastewater of 10.5~14.6℃ with 700 L/h flow rate as the heat source of heat pump. Meanwhile, maximum temperature drop of wastewater from the heat pump was 9.2℃ when the temperature of wastewater was above 10℃. Further more, with wastewater of 10.5~14.6℃ as the heat source, the heating cost of culturing water from 7℃ to 10~15℃ by heat pump was 0.36, 2.91, 5.86 and 5.68 Yuan/t, which less than that of heating by coal (oil, gas)-fired boilers and electricity, respectively. Meanwhile, the heating of culturing water by heat pump from 7℃ to 10~15℃ can also decrease CO2 emission of about 2.7~7.3 t annually than coal-fired boiler.