The utility model provides a heat dissipation device of an ultrahigh voltage transformer, comprising an oil tank, a cooler and an oil pump, wherein a transformer body is arranged in the oil tank; the oil pump is connected with an oil outlet of the cooler and an oil inlet of the oil tank; and an oil outlet of the oil tank is connected with an oil inlet of the cooler. The heat dissipation device of the ultrahigh voltage transformer is characterized in that an oil clearance is formed between the oil tank and the transformer body; and the cooling oil flows into the transformer body by the oil clearance. In the process of heat dissipation to the transformer, the heat dissipation device of the ultrahigh voltage transformer can reduce the flow speed of the cooling oil and avoid the phenomenon of discharge of oil flow.