The hot plasticity of Mnl8Crl8 high nitrogen austenitic stainless steel is studied using the thermal simulated test in this paper. In addition, microstructural evolution and precipitate morphology are investigated through optical microscope(OM), scan electron microscope(SEM), X-ray diffraction(XRD) and Electron probe micro-analyzer(EPMA). The results show that the area reduction of Mnl8Crl8 steel varies in a “V” shape in the elevated temperature region. It means that plasticity of Mnl8Crl8 steel is relatively low when the deformation temperature is in 1000~1100°C, whereas an excellent plasticity can be obtained in 850~950°C and 1150~1200°C. The peak value of area reduction appears at 1050°C. The analysis of SEM on fracture morphology indicates that the inter-granular fracture and dimple fracture occur at 1050°C and 1150°C respectively. The results of OM exhibit that the dendrite precipitation occurs while the precipitate in grain boundary solutions as the temperature increasing and the grain coarsens immensely beyond 1000°C. However, dendrite precipitate solutions into the austenite matrix at further elevated temperatures. It causes the plasticity substantial improvement in 1150~1200°C. Moreover, the observed precipitation of the steel is confirmed to be Cr23C6 by XRD and EPMA.