Abstract: A thermodynamic model to calculate nitrogen solubility in different phases of Fe-Cr-Mn alloy system was developed on the basis of earlier works and regular melt model. The calculation results of 18Cr-18Mn alloy showed that the nitrogen solubility in different phases increases with increasing nitrogen partial pressure, and the δ ferrite zone becomes smaller even disappears. So increasing nitrogen partial pressure can prevent the porosity forming during solidification. Increasing properly the contents of component elements of austenite in the melts, the δ ferrite zone where the nitrogen solubility is low becomes smaller even disappears during the solidification of the melt, thus decreasing the potential nitrogen precipitates during solidification. The calculation results are in good agreement with what were done in earlier works.