This application provides an in-vehicle communications system used in a vehicle. The in-vehicle communications system includes a control device, a plurality of gateway devices, and a plurality of communication endpoints. Each gateway device is communicatively coupled to the control device, and each gateway device is communicatively coupled to at least two other gateway devices. Each gateway device is further communicatively coupled to at least one communication endpoint. A gateway device or a controller is configured to: when receiving communication data of end-to-end communication, route the communication data by using a first communication link indicated by a local routing policy, and if the first communication link is abnormal, route a part or all of the communication data by using a second communication link. The system may be used in the field of assisted driving and self-driving.