Desalination with a humidification-dehumidification process has proven to be an efficient means of utilization the condenser and evaporator of heat pump to product fresh water from sea water. This paper presents an integrative device of air-conditioning and desalination driven by mechanical vapor compression heat pump. There were four circuits in this system such as vapor compression, heat water, air flow and fresh water circuit. According to different combination, several function including air-conditioning, dehumidification and desalination could be realized. Compared with traditional desalination device, the system utilized the heat from condenser and cold from evaporator of heat pump adequately, and reclaimed latent heat partially. The experimental results show that it would circulate with considerably higher PER under the optimal choice of sea water flow rate, feed water temperature, the volume of sea water in box and the length of humidifier. When this system was used as dehumidification, it can regulate air temperature of outlet in a large range.