An optimized method was proposed to improve the processing efficiency of Selective Laser Melting (SLM) for multi-parts. First, the time consuming of the SLM process was analyzed and the 2.5D nesting rules for the optimization were established to reduce the time consuming. Then, the 2.5D automatic nesting was studied. A simplified method which uses the 3D projection to convert the 2.5D nesting to the 2D nesting and an algorithm for generating the projection from slice data were presented. Finally,by taking a operation model for an example, an experiment was performed on the virtual SLM system developed with OpenGL and VC++ to simulate the motion of real system and to validate the feasibility of the method. The result shows that the processing times are reduced from 4 to 3, the recoating times are from 3 892 to 2 231 and the expected processing time has been from 91 276 s to 69 918 s at a scanning speed of 600 mm/s, slicing thickness of 0.035 mm and track space of 0.08 mm.The time consuming has been significantly reduced as compared with that before optimization.