<p>In this paper, the plasticity of stainless steel at high strain rate and high temperature has been studied by dislocation dynamics at medium and long scales. For the samples obtained in the SHPB dynamic impact test, the uneven distribution of high-density dislocations and more deformed twins were observed in the samples by EBSD and TEM. Based on the cross-slip mechanism of dislocations, the high-frequency active sliding system of stainless steel at high strain rate is analyzed by simulation and experiment. The double dislocation increases the strain-hardening rate. The plastic deformation at the same strain rate is mainly controlled by the active initial dislocation. Under high temperature conditions, the shear stress and critical distinguished shear stress change according to dislocation multiplication. As the temperature rises, it enters the second stage of strain hardening. The cross-slip is activated to annihilate the absorption dislocations, resulting in an inverse ratio between the initial temperature and the rate of rise of the dislocation density in this stage, and the strain-hardening rate increases with the increase of the initial temperature. At the same time, assuming different initial dislocations, this paper analyzes, at very high strain rates, the existence of yield stress independent of the strain rate which prevents the dislocation from moving. The simulation results are in agreement with the experimental data and provide insights into the study of stainless steel in extreme environments.</p>