Abstract: The study of the thermodynamic equilibrium of the liquid sodium hydrogen system is carried out on the basis of chemical engineering thermodynamics. The relationship between the hydrogen partial pressure above the surface of liquid sodium and hydrogen concentration in liquid sodium is presented. The quantitative dependence of the Sieverts constant on the temperature is obtained from above. And the experimental data of the Sieverts constant from some references are analyzed. Moreover,the temperature dependence of hydrogen solubility in sodium is given, and the comparison with the experimental data is made.