Abstract: 316L stainless steel powder was printed and molded by laser selective melting molding（SLM） with different process parameters. The tensile test and fatigue test were carried out on the formed powder. The fracture morphology was observed by SEM. The influences of process parameters on the microstructure defects and its fatigue mechanism were analyzed. The results show that different process parameters change the tensile strength and elongation of the section of the sample, which lead to the change of fatigue life.The influence of scanning distance on the tensile strength and elongation of the section is great, while that of laser power and scanning speed is relatively small. By comparative analysis, the optimal process parameters within the test range are obtained: laser power 320 W, scanning speed 910 mm/s and scanning spacing 0.15 mm. The tensile strength and fatigue life of the samples obtained under the optimal process parameters are better than those obtained under the traditional process, but the elongation of the cross section is less than that of the traditional samples,which means that the plasticity is poor. The fatigue life is related to the tensile strength, which increases with the increase of tensile strength.