There are numerous manufacturing processes used for metal powder production. Metal powders have been widely utilized in various industry applications, such as additive manufacturing, powder metallurgy, metal injection molding and shot penning etc. Although additive manufacturing has been recognized as having the highest value in metallurgical industry and thus become the key development projects in the world. However, there are rigorous requirements for the metal powder used in additive manufacture, such as the particle size, sphericity, oxygen content etc. In this research, powders of stainless steel and aluminum alloy were produced by high pressure gas atomization because of the advantages as high sphericity and high fluidity, low oxygen content and fine particle size with narrow distribution. Since the metal powders were produced through the high temperature melting and then fast-curing process, it is expected that the metal powder can achieve the fine microstructure and even possibly amorphous state. In this study, experimental equipment including four parts, which are melting, atomization, cooling and classification in sequence. In addition, we using supersonic nozzle with external mixing mechanism. Result shows that the average particle size of aluminum alloy is 28.9μm and stainless steel is 43μm. Furthermore, a high yield ratio of 95% of the powder aluminum alloy was obtained for the particles with size less than 65μm. It is also found that the powder exhibits excellent spherical shape. The dendritic microstructure of the metal powder is associated with the cooling rate during the processes. The particle size of stainless steel powder which is under 30μm has part of inconspicuous dendrites. The above results are observed in the surface morphology and crystallization patterns. In addition, the hardness of stainless steel powder is three times higher as compared with raw materials because of the fine microstructure achieved by the gas atomization process. It is concluded that this process can be used to produce the fine metal powder for additive manufacturing applications.