<p>In this study, the microstructure and mechanical properties of high-nitrogen austenitic stainless steel are improved by friction stir processing (FSP) technology. After FSP, three groups of processed sheets without surface defects were obtained, and they were defined as 600-60, 800-50 and 800-70, respectively, using a combination of rotation speed and feed speed. The optical microscopy (OM) and electron backscatter diffraction (EBSD) analysis show that the grains in the processing area are obviously refined after strong plastic deformation. The average grain size is reduced from 72.3μm of the original material to 8.3 ~ 11.3μm in the stir zone (SZ). The microstructure of the processing area is composed of uniform equiaxed grains and sufficient Σ3 twins. The microstructure evolution is attributed to twin-dominated dynamic recrystallization (DRX) and continuous dynamic recrystallization (CDRX) during shear plastic deformation with high strain rate. Among the three sets of parameters, the recrystallization degree of 800-50 sample was the highest. This should be attributed to the highest peak temperature (953.5 °C) obtained during processing, which promotes recrystallization nucleation and grain growth. The mechanical properties were tested at room temperature, and the results demonstrated that the mechanical properties of high-nitrogen austenitic stainless steel can be improved by FSP technology. Among, the 800-50 sample obtained the best comprehensive mechanical properties, i.e. the yield strength and ultimate tensile strength are increased from 524.8MPa and 910.4MPa of the original forged sample to 728.1MPa and 1063.7MPa, respectively. Due to the work hardening effect, the elongation decreased from 75.0% to 58.1%.</p>