The utility model discloses an intelligent ultrasonic hermetic cleaning device for a rigid main transformer radiator. The intelligent ultrasonic hermetic cleaning device comprises a rigid shell and a control circuit, wherein the rigid shell can be sleeved on the main transformer radiator; the rigid shell is formed by buckling a front half part and a back half part; the front half part and the back half part are locked together by adopting a connecting piece; a plurality of ultrasonic probes are embedded into the rigid shell body; a water inlet and a water outlet passing through the inner and outer walls of the shell are formed on the shell; a water inlet electromagnetic valve is arranged at the water inlet; a water outlet online conductivity gauge and a water outlet valve are arranged at the water outlet; each ultrasonic probe is connected with an ultrasonic generator; the control circuit is used for monitoring the electric conduction situation of cleaning liquid at the water outlet through the online conductivity gauge in order to control the work of the ultrasonic generator and the water inlet electromagnetic valve. According to the intelligent ultrasonic hermetic cleaning device, dead angles are not left, the phenomenon of water splashing is avoided, online cleaning without power outage is realized, and the main transformer radiator can be cleaned safely, efficiently, cleanly and rapidly under the condition of the electric running state of a main transformer.