Abstract: This study investigates the effects of annealing processes on the microstructure and mechanical properties of 321 stainless steel ultra-thin strips. In the experiment, 321 stainless steel ultra-thin strips with different cold rolling reductions were adopted. By setting different annealing temperatures and holding times, combined with two cooling methods（furnace cooling and air cooling）, the influences of heat treatment processes on the microstructure and mechanical properties of the experimental strips were explored. The results show that with the increase of annealing temperature, the yield strength of the strips decreases while the elongation increases, indicating that high-temperature annealing is conducive to improving the plasticity of the strips. Short holding time and rapid cooling are favorable for obtaining fine and uniform austenite grains, thereby enhancing the synergistic effect of strength and plasticity of the strips. In contrast, long holding time and slow cooling promote the precipitation of M₂₃C₆ carbides and σ phase, which increases the hardness of the strips but leads to the reduction of their plasticity. Through comprehensive consideration, the heat treatment process consisting of 1 050 ℃ annealing temperature, short holding time and rapid cooling can effectively improve the comprehensive mechanical properties of 321 stainless steel ultra-thin strips.