In this study, a novel solar assisted heat pump desalination unit for drinkable water is proposed and Investigated experimentally. The experimental unit, which mainly consists of compressor, condenser, evaporator, packing humidifier, centrifugal fan, precooler and seawater tank, et al., was designed and fabricated. The effects of the cooling seawater, the process air, the mixture ratio (the ratio of the remaining seawater flow rate from the humidifier to total hot seawater flow rate) and the thermodynamic cycle on the system performance were investigated. The experimental results show that there exists the optimal flow rate of the process air corresponding to the studied unit under given conditions. The maximum productivity of the unit is 12.38 kg/(kWh) when the flow rate of cooling seawater and process air are 0.3 m(3)/h and 450 m(3)/h respectively, which is higher than those of other solar assisted heat pump desalination units in previous works. A big mixture ratio is preferred for improving the system performance. A further performance comparison between open cycle and closed cycle indicates that the yield of the open cycle increases with the increase of the cooling seawater flow rate, which is opposite to that of the closed cycle.