The equilibrium concentrations of SiHCl3 and SiCL, in the SiCl4-H (2) system are investigated on the basis of thermodynamic data for the corresponding pure compositions under specified thermodynamic parameters. Eight independent reactions in the SiCl4-H (2) system for hydrogenation of SiCl4 to SiHCl3 are obtained. Furthermore, the factors (such as temperature, pressure, and feed mole ratio) influencing the equilibrium concentrations of SiCl, and SiHCl3 are studied. Diagrams of the equilibrium concentrations of SiCl4 and SiHCl3 as a function of temperature, pressure, and feed mole ratio are presented. Finally, the optimal thermodynamic conditions in the SiCl4-H-2 system for hydrogenation of SiCl4 to SiHCl3 are determined to be 1,100 degrees C, 0.3 MPa, and a feed molar ratio of 4. Under these conditions, the conversion ratio of SiCl4 to SiHCl4 is about 25%, compared to a value of less than 20% in actual production.