The invention relates to an onboard atomizing cooling system for creating a negative pressure environment by virtue of an ejector, which belongs to the field of cooling of onboard high heating density equipment, and mainly solves the high heating density continuous heat dissipation problem of the surface of onboard electronic equipment. The onboard atomizing cooling system mainly comprises a water tank (1), a water pump (2), a flow adjusting valve (3), a stop valve (4), a flow meter (5), a nozzle (6), a to-be-cooled surface (7), an atomizing chamber (8), a pressure meter (9), an engine tail gas entraining hole (10), an ejector nozzle section (11), an ejector mixing section (12), a exhausting hole (13), a heat pipe heat exchange box (14), an external environment hole (15) and a heat pipe (16). According to the onboard atomizing cooling system, engine tail gas is taken as an ejection air source, the negative pressure environment is created in the atomizing chamber, the surface of high-temperature electronic equipment is atomized and cooled by virtue of vaporization latent heat of water, and the cooling of the heat pipe and the heat-exchanged water vapor on the surface of the to-be-cooled surface are introduced, so that the closed atomizing cooling system can safely and stably work, has an energy-saving effect and can meet the cooling requirements in onboard complex environments.