The invention provides a method for recognizing messages in a CMC system in a CM online process. The method comprises the steps that all messages, except DHCP messages, with the source address being a CM or the destination address being the CM are recognized as TFTP messages; then, the messages are subjected to VLAN Tag treatment, VLAN Tags are added for upstream messages, VLAN Tags are deleted for downstream messages, and thus TFTP interaction between the CM and a configuration server is completed, and configuration files needed by initialization of the CM are downloaded. According to the method, the content of TFTP messages does not need to deeply analyzed, source MAC or destination MAC information in message heads is extracted to be compared with MAC addresses recorded in CM information sheet items, messages with the same MAC and without VLAN Tags are recognized as the TFTP messages, the processing logic is simple and easy to achieve, and the forwarding performance of CMC is not influenced.