Gas atomization is one of the earliest technologies to prepare spherical metal powder,which strongly supports the development of additive manufacturing. Due to the complexity of the powder formation process,it is impossible to observe and study directly. Therefore,simulation becomes the best way to study the gas atomization process and the powder formation mechanism. The theoretical models of gas atomization are summarized,including gas velocity distribution,breakup mechanism and the spheroidization,flight,solidification of liquid droplets. The effects of melt properties and process parameters on the powder formation are also discussed. Finally,the development trends of the theoretical models of gas atomization are pointed out.