Hot air brazed stainless steel core plates made from S30403 austenitic stainless steel exhibit outstanding mechanical properties and environmental friendliness. Compared with conventional hot radiation brazing， the hot air copper brazing technology increases productivity and reduces processing costs by more than 30%. Stainless steel is subjected to high speed and high temperature （1 100 °C） hot air treatment during the copper brazing furnace， which affects the mechanical properties of stainless steel. The tensile test of hot air brazed S30403 austenitic stainless steel under high temperatures and after cooling from high-temperature was carried out， and the main mechanical properties such as elastic modulus， nominal yield strength， ultimate strength， elongation after break were obtained. A calculation model of main mechanical properties at high temperatures of hot air brazed S30403 was established， and a high temperature stress-strain constitutive model was established based on the Rasmussen model. The study shows that the initial modulus of elasticity， nominal yield strength and ultimate strength of hot air brazed S30403 austenitic stainless steel at high temperatures decreases with the increasing temperature. At 900 °C， modulus of elasticity is about 39% of that at room temperature， nominal yield strength is about 20% and ultimate strength is about 10%. The cooling mode has a minimal effect on the nominal yield strength and the ultimate strength of hot-air brazed S30403 austenitic stainless steel， but it has a more significant impact on the modulus of elasticity and elongation after break.