The invention relates to a method for synthesizing p-acetamido benzene sulfonyl chloride by phosphorus pentachloride, relating to the preparation method for sterilization and mould inhibition midbody of sulfonamides. The invention takes acetanilide and chlorosulfonic acid as raw materials, uses phosphorus pentachloride as chlorinating agent; under the action of organic dissolvent, the raw materials are sulfonated, chloridized, separated, and washed to obtain the product. The invention has the effects of little chlorosulfonic acid usage, high product yield, few generated waste acid,, completely cycling dissolvent, recycled by-products, low manufacturing cost, being convenient to popularize and apply, and the like. The products prepared by the method can be widely applied to the preparation of the sterilization and mould inhibition of sulfonamides and industries such as coating, plastics, pesticides, etc.