The present invention discloses a packet processing method, which applies to a high-performance and scalable flow processing system architecture. The service board performs security processing for packets received from external devices by using the firewall function before sending them to the main CPU; similarly, the service board also performs security processing for packets sent from the main CPU by using the firewall function before the main CPU sends them to external devices. The methods of the present invention utilize high performance and good scalability of the new architecture. In a network with heavy and high-speed traffic, the service board performs security processing for packets by using the firewall function and then transmits the valid packets to the main CPU. Thus, the main CPU is protected by the firewall function against attack packets.