Applications of thionyl chloride in pharmaceutical and pesticide sectors and application developments in organic synthesis reaction and ring formation reaction are introduced. Synthesis methods of thionyl chloride such as HSO 3Cl method, SO 2 method, SO 3 method, co production method and enterprises adopting above methods are evaluated. The domestic production, demand, import and export of thionyl chloride are analyzed. It is suggested that backward HSO 3Cl method should be eliminated and new plants should adopt advanced technologies. Factors such as feedstock source and scale effect should be considered when new plants are being built.