The invention discloses an automatic fire-extinguishing system of an automobile engine cabin, which comprises a fluid reservoir, an electric control water pump, a pressure opening valve, an air release valve, an injection track, an alarm lamp, an ECU, a smoke sensor, a manual control circuit and the like, wherein the main principle is that a matrix smoke sensor of a forecabin automatically monitors the fire situation of the forecabin, once the forecabin starts to smoke, the sensor immediately inputs signal to the ECU, the ECU immediately starts the water pump to inject a fire-extinguishing agent through a fire-extinguishing agent track to all the parts of the forecabin to quench, an oil line is simultaneously and actively quenched and protected, and thereby the automatic fire-extinguishing system can eliminate danger when the fire danger is initially generated, prevent the fire from rapidly spreading to an oil tank along the oil line so as to protect the safety of people, and under the condition of failure extinguishment, the automatic fire-extinguishing system can give passengers more time to escape. In addition, when on fire, sometimes a wire harness may be on fire, at this time, an automatic control may fail to work, the alarm lamp does not light, but a driver can find out the sign of a fire and even smells the pungent smoke, so a manual switch is pressed down, and a fire-extinguishing device can also start to extinguish.