A packet transmission method and a frame-shaped communication device are disclosed. The packet transmission method is applied to the frame-shaped communication device. The frame-shaped communication device includes a first MPU, a second MPU, and an LPU. The first MPU is connected to the LPU through a first transmission channel. The second MPU is connected to the LPU through a second transmission channel. During packet transmission, a service flow packet is transmitted through the first transmission channel, and a non-service flow packet is transmitted through the second transmission channel. Therefore, the service flow packet and the non-service flow packet are transmitted through different transmission channels, and are processed by different MPUs, so that the service flow packet and the non-service flow packet do not compete with each other. In this way, transmission efficiency of the non-service flow packet is improved. In addition, when the first MPU is attacked by an abnormal service flow packet, the second MPU is not affected, and may normally perform operation and maintenance management.