The invention belongs to the field of medicinal preparations, and discloses a method for preparing phloroglucinol injection. The method for preparing the phloroglucinol injection comprises the following steps of: (1) preparing solution containing phloroglucinol and trimethyl phloroglucinol; (2) stirring the solution uniformly and then filtering the solution for sterilization; (3) encapsulating the filtered solution by a conventional method and sterilizing the encapsulated solution, wherein the temperature for the sterilizing filtration in the step (2) is 5 to 40 DEG C, and preferably 10 to 35 DEG C. The technical scheme can ensure stable content of the trimethyl phloroglucinol during the preparation of the phloroglucinol injection. Meanwhile, the method for preparing the phloroglucinol injection ensures the sterility assurance level of the injection by using the sterilization process with over sterilization effect.