This paper presents an open air-vapor compression refrigeration system for both air-conditioning and desalination on ship cooled by seawater, and proves its feasibility through performance simulation. Pinch technology is used in the analysis of heat exchange in the surface heat exchanger and the temperature difference at pinch point is selected as 6 degrees C. The freshwater is obtained from the dehumidification of the compressed wet air before turbine and the flash and condensation of the cooling water. Its refrigeration depends mainly on both air and vapor, more efficient than a conventional air-cycle, and the use of turbo-machinery makes this possible. This system could use the cool in seawater, which could not be used to cool air directly. Also, the heat rejected from this system could be used for desalination. The sensitivity analysis of COP to eta(c) and eta(t) and the simulated results T-4, T-7, T-8, q(1), q(2), and w(m) of circle are given. The simulations show that the COP of this system depends mainly on T-7, eta(c), and eta(t), and varies with T-3, or T-wet and that this circle is feasible on ship although the sensitivity of COP to efficiencies of the axial compressor and turbine. The optimum pressure ratio in this system could be lower and this results in a fewer number of stages of axial compressor. The adoption of this system will make air-conditioned room more comfortable because of its very low temperature air obtained. Humid air is a perfect working fluid for central air-conditioning and desalination on ship and no cost to the owner. The system is more efficient because use of cool seawater to cool the air before turbine. In addition, Pinch technology is a good method to analyze the wet air heat exchange with water.