The product quality of selective laser melting (SLM) is closely related to the alloy powder characteristics; including the size distribution and the oxygen content. In this work; the 316L stainless steel powder was prepared by a vacuum atomization furnace and sieved into a normal-sized distribution range from 15 to 53 μm with a median diameter of 37.4 μm; and a fine-sized distribution range from 10 to 38 μm with a median diameter of 18.9 μm. Then they were mixed with each other in different proportions. The results show that; under the condition of the same SLM parameters; the SLM part; with adding a large amount of fine-sized powder; has a lower density and strength; as well as more holes and spheroidized particles; compared with the SLM part with adding a small amount of finer-sized powder. Furthermore; the 316L stainless steel powder with a high oxygen content was prepared by a non-vacuum atomization furnace. Although the 316L stainless steel powder with a high oxygen content can be evenly spread in the SLM process; the surface layer of the powder is easy to form an oxide film during the cooling and solidification of powder inside the molten pool. Under the action of thermal stress; the small crack forms and expands along the oxide film; eventually leading to large cracks inside the melt channel.