The invention relates to a spraying agent type automatic fire extinguishing device for a vehicle, which is suitable for an engine room of a minicar. The spraying agent type automatic fire extinguishing device comprises a cylinder body, a superfine dry powder spraying assembly and a spraying agent box assembly and is vertically or horizontally arranged in the engine room of the minicar through a hoop; the superfine dry powder spraying assembly is arranged as a nozzle assembly connected with an upper opening of the cylinder body during vertical installation; a lower cover is connected with the spraying agent box assembly and seals a lower opening of the cylinder body; a compound type superfine dry powder extinguishing agent with mean grain size less than or equal to 5 micrometers is filled into a cavity of the cylinder body; the nozzle assembly comprises a protecting hood, a taper pipe nozzle nipple, an aluminum film and a sealing gasket which are connected; the spraying agent box assembly comprises a spraying agent box body, a protective film and a nozzle; the side wall of the spraying agent box body is provided with a through hole and the protective film; the lower cover is provided with a through hole for guiding an electric igniter and is connected with a control circuit; the side wall of the cylinder body which is horizontally arranged is provided with the through hole, andthe cylinder body is also used as the superfine dry powder spraying assembly. The spraying agent type automatic fire extinguishing device has multiple starting ways and extinguishing time less than 3seconds, is suitable for various natural environments with the minicar and can stably work.