A method for manufacturing a battery module is disclosed herein. In some embodiments, a method for manufacturing a battery module which comprises a module case, in which an internal space is formed by a bottom plate and sidewalls, and an injection port is formed in the bottom plate or the sidewalls; a plurality of battery cells existing in the internal space; and a resin layer in contact with the bottom plate or the sidewalls while being in contact with the battery cells, the method including attaching a tape to cover the injection port of the bottom plate or the sidewalls; mounting an injection device of a resin composition such that the injection device is mounted on the injection port while penetrating the tape, and injecting the resin composition into the mounted injection device. The method provides a simple process and at low cost without occurrence of a reverse discharge phenomenon.