The invention relates to a mechanism of measuring a top oil temperature of a transformer. The mechanism of measuring the top oil temperature of the transformer comprises a transformer body which comprises a box body, a box cover and a body; an insulating end ring is arranged on a winding of the body; a pressure plate is arranged on the upper portion of the insulating end ring; a pressure plate oil permeable through hole is formed in the pressure plate; an upper yoke is also arranged on the body; an iron core clamp is also arranged on the right side of the upper yoke; the iron core clamp presses the pressure plate; a gasket is also arranged on the pressure plate; a cushion block oil permeable through hole is formed in a cushion block; a supporting plate is also welded to the right side of the iron core clamp; the supporting plate presses the cushion block and a temperature measuring device is fixed thereon; a temperature sensing head of the temperature measuring device extends into the oil permeable through hole. According to the mechanism of measuring the top oil temperature of the transformer provided by the invention, the measured oil temperature is the oil temperature of the upper end portion of the winding. The measuring result is high in accuracy, the risk of local overheating of the transformer is avoided, no special demands on a basic structure of the transformer are put thereon, and the mechanism is convenient to mount and suitable for large-scaled application.