High purity anhydrous InCl3 was prepared by direct chlorination method, and the optimum reaction temperature was 600℃. The trend and degree of reaction in the system were clarified by Gibbs function and equilibrium partial pressure based on equilibrium thermodynamics. Meanwhile, thermodynamics calculation further showed the main products generated at different temperatures. The analysis result indicated that the major species of indium chloride was In2Cl6 which could immediately decompose to InCl3 and other by-products with the temperature of system below 665℃ and being InCl3 with the temperature above 665℃, and experimental result showed an approximately 65℃ deviation between experimental and computational result, indicating the difference between equilibrium status and non-equilibrium status during the reaction process.