Abstract: A new thermodynamic model was developed to calculate the nitrogen solubility in molten stainless steel, in a wide range of system temperature, nitrogen partial pressure and alloying constituents by introducing an interaction coefficient expressing the effect of nitrogen partial pressure on nitrogen activity coefficient on the basis of experiments and other authors' earlier works. The calculation results were in good agreement with measured values, with which the influences of nitrogen partial pressure, temperature and alloy constituents on the nitrogen solubility in molten stainless steels were discussed. Under high pressure especially the high concentration of alloying elements, it was found that the relationship between nitrogen solubility in liquid stainless steels and nitrogen partial pressure doesn't follow Sievert's law. The dependence of temperature on the nitrogen solubility is determined by the composition of alloying elements under a certain nitrogen partial pressure. The mass fraction of nitrogen in the 20%Cr-20%Mn alloy can be up to 0.8% at 1873 K under normal pressure (N2 partial pressure = 0.1 MPa).