Abstract: In laser selective melting, the forming of powder bed will significantly affect the subsequent process and the quality of final products. In this paper, the dynamic numerical simulation of powder spreading behavior and forming quality in SLM forming process is carried out by using discrete element method (DEM). The influencing factors of powder bed quality are studied from two aspects of density and uniformity. The results show that the effect of powder spreading speed on the quality of powder bed is obvious. The powder spreading speed, powder spreading angle, scraper clearance height and powder particle size all have an important influence on improving the average density and uniformity of the powder bed. The lower the powder spreading speed, the higher the quality of powder bed and the lower the working efficiency. With the increase of the clearance height of the scraper, the density of the powder bed increases and the uniformity of the powder bed decreases to a lower value. The density of powder bed increases with the increase of powder laying angle, and then decreases. The structural uniformity of the whole powder bed also has a similar change trend. Increasing the particle size of powder will reduce the density of powder bed and the uniformity of powder bed structure. The powder spreading speed is 0.1 m/s, the clearance height of scraper is 90 μm. The powder spreading angle is 15°, and the powder particle size is 15 μm, the powder bed forming quality is the best. The research results of this paper will provide a valuable reference for the formation of high-quality powder bed in SLM process.