As a representative of the fourth generation refrigerant, water has numerous advantages, such as non-pollution (ODP=0, GWP<1), accessible, low-cost, secure, stable and large latent heat of vaporization, which can completely satisfy the requirements of the environment as a refrigerant. However, low molecular weight, large specific volume and high adiabatic index of water vapor determine that the water vapor systems have the characteristics of small differential pressure, large compression ratio, small unit volume capacity, large volume flow and high discharge temperature. It also puts forward higher requirements for water vapor compressors, which seriously limit the use and promotion of water as a refrigerant. Currently, the water vapor compressors mainly are centrifugal, screw and roots compressor. Centrifugal water vapor compressor has the advantage of large volume flow rate, but it has small single stage compression ratio, high discharge temperature and droplet sensitivity. At the same time, the blade and shell material of the centrifugal water vapor compressor are severe and expensive. Therefore the centrifugal water vapor compressor is suitable for the largest volume flow rate and smallest compression ratio system. Screw water vapor compressor has the advantages of good stability, large compression ratio and wet compression; however the volume flow rate is smaller. It is more suitable for the refrigeration system with small volume flow rate and large compression ratio. Roots water vapor compressor has the advantages of less vibration components and simple structure, however it also has small compression ratio, so it is usually used in the medium heating capacity and large temperature rise systems. In order to promote water refrigerant to be wildly used in production and livelihood field, researching and developing practicable compressors for different usage occasions and steam requirements is an interesting and significant research project in future.