Abstract: Aiming at the process of forming micro melting pool of stainless steel powder by laser melting in the selected laser melting process, the influences of laser power, spot diameter and heating time on the melting speed, temperature field and size of micro-molten pool were studied by numerical simulation method. The simulation results show that increasing laser power and heat flux can effectively promote the melting and heat transfer of the materials. The temperature field and pool formed by laser with large spot diameter are wide and shallow, while the temperature field and pool formed by small spot diameter are narrow and deep. By comparing several groups of data, it is concluded that the powder material can be fully melted and the forming defects can be reduced by reasonable ratio of laser power and spot diameter, thus the quality of the parts improves.