Using the method of equation of state (phi-phi) the model of vapour-liquid phase equilibrium for the industrial conditions (T, p, x, y) of ammonia outdropping from the post-reactor gases was developed. Satisfactory results were obtained for Redlich-Kwong-Soave-Stryjek-Vera and Peng-Robinson equation of state. Algorithm of the VLE determination (flash type), according to the above models, used as an element of the own simulation software for ammonia line "TAWAS" has been supplemented with a new semi-empirical procedure for the reduction of computational erros of ammonia concentration in gaseous phase because of it＇s technological importance.