The present disclosure relates to the technical field of payment terminals and provides a method and a device for upgrading a module firmware of a POS machine in order to improve safety of the POS machine when upgrading the module firmware. The method comprises: downloading a module firmware upgrade package; verifying a signature of the module firmware upgrade package; and decompressing the module firmware upgrade package to perform subsequent upgrading of a module firmware if a verification of the signature of the module firmware upgrade package is successful, or otherwise, returning information that the verification fails.