In this paper, 316L stainless steel samples were formed using the selective laser melting (SLM) technology to analyze the dynamic mechanical properties of the SLM 316L stainless steel under impact load. The quasistatic and dynamic compressive mechanical properties of the sample were tested using a universal experimental machine and a split Hopkinson pressure bar (SHPB) experimental device. Meanwhile, the test results of the SLM 316L samples were compared with that of the 316L stainless steel formed via traditional methods. The internal relationship between the microstructure and mechanical properties of the material was analyzed through the micromorphological observation. Finally, the Johnson-Cook (J-C) constitutive model was established to predict and characterize the dynamic mechanical behavior of SLM 316L stainless steel. The experimental results show that the SLM 316L stainless steels show typical elastic–plastic characteristics and significant strain rate hardening effects in mechanical experiments. Moreover, compared with traditional 316L, SLM 316L has a higher hardening modulus at the dynamic strengthening stage because of the cellular structure with micron size. The yield strength of the cold-rolled 316L sample is higher because of the residual stress caused by plastic deformation. By modifying the basic J-C model using the experimental data, the dynamic mechanical behavior of SLM 316L can be described more accurately.