The invention relates to an oil-immersed power transformer top layer oil temperature monitoring method based on thermosensitive resistance and belongs to the technical field of photoelectron measurement. According to the method, firstly, a thermosensitive resistance temperature sensor is connected with a universal meter, and the thermosensitive resistance temperature sensor is inserted into top layer oil of a transformer through a test hole of the oil-immersed power transformer; after the temperature sensor is stable, the resistance value of a thermosensitive resistor is measured by the universal meter; then, the top layer oil temperature of the oil-immersed power transformer is calculated through a resistance and temperature change relational expression; and finally, the measured temperature is compared with the temperature rise standard of the oil-immersed power transformer, and whether the oil-immersed power transformer is under the normal work condition or not can be judged. The method has the advantages that the thermosensitive resistance temperature sensor can be inserted into the top layer oil of the oil-immersed power transformer for a long time, and the temperature of the top layer oil of the oil-immersed power transformer can be detected in real time; and the structure is simple, and the operation is convenient.