The calculated values of the formation enthalpy, ΔH2980, and the free energy of formation, ΔG2980, of platinum compounds and some related phosphate or metaphosphate compounds in phosphate laser glass were given based on the thermodynamic and electrochemisty methods in the present paper. Using the parameters mentioned above, the direction and limitation of chemical reaction between liquid and solid, gas and solid, or gas and liquid that can possibly exist in phosphate laser glass during the melting process were studied. Finally, the mechanism of eliminating platinum inclusions in phosphate laser glass by POCl3 gas bubbling and the optimum process were discussed from thermodynamics aspect.