The invention relates to a method and circuit for auxiliary vehicle-mounted equipment to precisely recognize ACC state. A voltage regulating property of a voltage-regulator tube and a voltage dividingproperty of a resistor are used, an AD collecting method is adopted to realize the detection of the ACC state, ACC is processed under different state, normal starting and closing of equipment are realized, the circuit is simple, the cost is low, and the precision of the state detection is high; and the deficiency that an ACC threshold value is hard to set due to the fact that external factors exist is overcome, the precision of setting of the ACC threshold value is improved, the controllability is high, the stability is high, and the circuit has universality. According to the method and circuit for the auxiliary vehicle-mounted equipment to precisely recognize the ACC state, serial port communication and SPI communication are adopted to realize data interaction, on-off state of the equipment is controlled in real time and real-time state alarming is carried out, and the stability of a system and intelligence of the equipment are improved; and in the installing process of the equipment, whether the AC state is abnormal or not can be rapidly detected and voice alarm is carried out, meanwhile, the equipment is turned off as usual, the condition that the equipment can be normally turned off under the abnormal state of ACC OFF is ensured, and unnecessary power consumption of a battery on a vehicle is prevented.