The embodiment of the invention discloses a controller fault replacement system and method, and the system comprises a first communication bus, a second communication bus, a vehicle communication network, a main controller, and at least one auxiliary controller, and the auxiliary controller receives controller operation data transmitted by the main controller through the first communication bus. External controller data transmitted by the vehicle communication network is received through the second communication bus, so that data sharing between the main controller and the auxiliary controller is realized, data synchronization between the main controller and the auxiliary controller is always kept, and when the main controller detects that a preset switching fault occurs, the main controller is switched to the auxiliary controller. Due to data synchronization of the main controller and the auxiliary controller, the auxiliary controller can be immediately switched to replace the main controller to transmit controller operation data to the vehicle communication network through the second communication bus, replacement of the auxiliary controller during downtime of the main controller is achieved, the stability of the controller is guaranteed, and vehicle function abnormity caused by downtime of the controller in the use scene of the vehicle is avoided.