The utility model relates to the field of transformer condition monitoring and condition-based maintenance, in particular to a transformer equipped with built-in sensors. The transformer comprises a transformer body and the built-in sensors, and the transformer body consists of an oil tank, an upper clamping piece, a lower clamping piece, a cushion block, an iron core and a winding; ultrasonic supports are arranged on the high voltage side of a long axial surface and the two short axial surface of the transformer body; six ultrasonic sensors are arranged inside the ultrasonic supports; the ultrasonic supports are installed and fixed through ultrasonic sensor fixing brackets arranged on the inner wall of the oil tank; three vibration sensors are arranged on the upper clamping piece and the lower clamping piece; and a high frequency current transformer (HFCT) is arranged at the place of an iron core grounding wire inside the transformer body. According to the utility model, the flexibility and the effectiveness of online monitoring are further improved and the operational safety level of the transformer is improved.