The invention discloses a vehicle-mounted multimedia audio system test method and device, and a vehicle-mounted multimedia system. The vehicle-mounted multimedia audio system test method comprises the following steps: obtaining a test starting instruction emitted from a user, and generating a key node signal test instruction according to the test starting instruction; according to the key node signal test instruction, successively obtaining the signals of N key nodes, and independently testing the signals of the N key nodes; according to a received pin state test instruction, obtaining the state information of other pins, except the pin which outputs a control signal, of a first processor, and independently testing the state information of other pins; and according to a received register state test instruction, obtaining the state information of other registers, except the register of which the storage information is revised, of a second processor, and independently testing the state information of other registers. The troubleshooting time of the vehicle-mounted multimedia audio system can be greatly shortened, and a troubleshooting range can be reduced to a maximum degree.