Abstract: The 0Cr18Ni9 austenitic stainless steel sheet with 0.2 mm thickness was welded in capacitor discharge spot welding.The temperature field and cooling rate of nugget was calculated.The results show that the joint microstructure consists of nugget zone and semi-melt zone.Due to very short time in welding, the cooling rate of the joint reaches to 5.1×10⁶ K/s, the growth of austenite microstructure is impeded, and the microstructure of the nugget is refined, which has rapidly solidified characteristics.As the austenite microstructure of the nugget stays in temperature province of activation with very short time, the chrome of austenite grain boundary precipitations is checked.To obtain the high quality spot-weld joint, the welding parameters are determined as: welding voltage 80 V, capacitor 6 600 μF and electrode pressure 18 N.