In cold spraying process, particle velocity has been commonly regarded as the key factor which influence the deposition efficiency and properties of the coating. In the present paper, stainless steel and aluminum were studied about influence of gas pressure and temperature on the particle velocity which was measured with DPV-2000 system. Deposition efficiency and micro-hardness of the coating also were measured. The microstructure of the coating was observed using optical and scanning electron microscopy. The critical velocity of the two materials was estimated based on the experiment results. It was shown that gas temperature had significant influence on the  critical velocity and coating properties.