The invention discloses a firewall implementation method applied to software defined networking. The firewall implementation method includes the steps that an SDN controller is started, the SDN controller and interchangers to be registered to the SDN controller send openflow protocol messages to each other, and the IDs of all the interchangers are obtained; the SDN controller starts the firewall functions of the registered interchangers, an initialization module of a firewall writes initial flow table items to the corresponding interchangers, and all the messages passing through the interchangers are discarded; the SND controller issues firewall rules to a certain registered interchanger, a message filtering module of the firewall issues different flow table items to the corresponding interchangers for achieving the rules according to the rule types, the SDN controller deletes a certain firewall rule of a certain registered interchanger, and a message processing module of the firewall deletes the corresponding flow table items of the corresponding interchanger. The firewall implementation method is applicable to firewall implementation of all types of SND interchangers, issuing and deleting of the firewall rules are achieved, and universality is achieved.