The blade inclination plays a significant role on the powder spreading behavior during the selective laser melting process. In this paper, a discrete element numerical model is established to investigate the powder spreading process and quality with different blade inclination angles. A quantitative indicator was proposed for different blade inclination angles to comprehensively evaluate the packing density and uniformity of the powder layer and the influence law of blade inclination on deposition quality is obtained. Based on the particle distribution and motion characteristics, the particle heap is divided into four zones including bottom layer zone, slope zone, blade influence zone, and internal zone. The powder spreading dynamic mechanism is comprehensively analyzed for the four regions, including particle trajectories and velocity fields, the shear band in front of the blade, and the distribution and evolution of inter-particle forces. It is found that when the inclination angle is less than zero, it is difficult for the particle heap to form a complete circulating flow, the shear band is relatively small, fewer particles flow towards the deposition layer, the packing density of powder layer decreases, fewer strong force chains between particles form, and force arches are easily formed in front of the blade gap, leading to particle jamming and the formation of voids. Therefore, the density and uniformity of deposition layer are poor. When the angle is greater than zero, the circulating movement of particle system is adequate, the shear band is larger, and more particles flow to the deposition layer, and the packing density of powder layer increases. As the inclination angle increases, the strong force chains increase, and the compaction effect of the blade is enhanced, which is beneficial for improving the density and uniformity of the deposition layer. This study provides a theoretical reference for the process parameter optimization and powder bed quality improvement.