The utility model discloses a heavy-duty car engine spontaneous combustion preventing device which comprises an engine water tank and is characterized by further comprising a bottom plate, a sprayingmechanism and a connecting water pipe. The spraying mechanism comprises a water inlet pipe; and the other end of the connecting water pipe is connected with the water inlet pipe. The utility model hasa reasonable structure, the device is simple to manufacture, small in size, convenient to use and low in cost, does not occupy the space of other parts of the vehicle engine compartment, can effectively prevent and control fire expansion in advance when the heavy-duty vehicle engine compartment has a spontaneous combustion phenomenon or the temperature in the engine compartment is too high, reduces the spontaneous combustion loss of the mining vehicle, and has good economic benefits and strong practicability.