The invention provides a CAN (Control Area Network) message anomaly detection method. The method comprises the following steps of building connection with an OBD-II port of a vehicle and receiving a CAN frame from the OBD-II, judging whether the frame format of the CAN frame is correct, and discarding the CAN frame and giving an alarm if the frame format of the CAN frame is wrong, further calling a detection function to carry out legality detection on the CAN frame if the frame format of the CAN frame is correct, and judging the CAN frame to be abnormal and giving an alarm if the CAN frame is illegal. The CAN message anomaly detection method is simple, high efficient, high in safety and high in practicality. The invention also provides a CAN message anomaly detection system.