Melting tracks and fusion surfaces formed by the “line by line-layer by layer” scanning in selective laser melting can greatly affect the quality of the product. Based on the process principle of selective laser melting, the optimized range of line energy density was obtained by single line scanning. The mesoscopic surface morphology of overlapped melting tracks formed by multi-line scanning was further analyzed by combining the average re-melting rate. Results show that the melting tracks are relatively continuous and the line width is relatively uniform when the linear energy density is between 0.070 and 0.217 J/mm. Small average re-melting rate of multi-line scanning will result in large surface height difference, and if the average re-melting rate is too large, the surface cracks will occur. When the average re-melting rate is between 18% and 50%, a relatively smooth surface can be obtained.