Based on the hot deformation behavior of selective laser melting forming 316L stainless steel at temperatures of 900~1 100 ℃, strain rates of 0.001~1 s-1was investigated by using the Gleeble-3800 thermal simulator. The results show that the flow stress decreases significantly with the increase of deformation temperature or decrease of strain rate during the deformation process. The strain-modified Arrhenius constitutive model is established for the whole deformation process, and the accuracy of the model is evaluated by using statistical parameters. The R-value of the model is 0.988 63 and the average absolute relative error of the model is 5.45%. The hot processing map of SLM forming 316L stainless steel at the strain of 0.9 is drawn, combining with microstructure analysis in different processing areas indicated that the instability mechanism is the formation of adiabatic shear zone and flow localization, and the optimal working conditions for SLM forming 316L stainless steel is low strain rate and high temperature strain rate area.