Abstract: To solve the problem of green part density inhomogeneity caused by powder-binder phase separation during metal powder injection molding, the numerical simulations were carried out using Moldflow 2023 software to investigate the effects of gate positions on melt flow behavior and powder volume fraction distribution in stepped part cavity. A three-dimensional simulation model of the stepped component was established and the mesh-independence verification was completed. Four gate schemes were designed, including thick-wall center, thick-wall upper end, thick-wall lower end, and thin-wall center. The temperature field, velocity field, shear-rate field, and powder volume-fraction distribution during filling were analyzed based on the suspension balance model. The results show that, the binder gathering near the gate and the powder segregation near mold wall and stepped structure occur for all gating schemes. The gate position changes the initial melt flow direction, so as to adjust the shear-rate distribution and the degree of powder-binder separation. The stepped structure forms the flow dead zones and shear-rate gradients, which induce the shear-induced particle migration and aggravate the local powder segregation. The scheme with gate located at the upper end of thick wall achieves the most uniform powder volume-fraction distribution, whereas the scheme with gate at thin-wall center suffers the high risk of cavitation defects at step corners during filling.