The present disclosure provides a system and a method for measuring hot-spot temperature of a transformer, wherein the measurement system comprises a processor, an oscilloscope and a plurality of ultrasonic sensors, wherein the ultrasonic sensors are oppositely arranged on an outer wall of a transformer oil tank and electrically connected with the oscilloscope, and the oscilloscope is electrically connected with the processor; the ultrasonic sensors receive signals transmitted by the oppositely arranged ultrasonic sensors and transmit them to the oscilloscope. The method, by applying an ultrasonic wave to measure the hot-spot temperature of a transformer in real time, solves the problems that methods in the prior art are susceptible to the external environment, have short service life and cannot correctly measure the internal temperature of the transformer.