In order to solve the problem that the resolution of the transformer windings ultrasonic detection system decreases with the increasing detection distance, this paper proposes a combined algorithm of ultrasonic synthetic aperture arc scanning, so that the resolution of the detection system is only related to the transducer itself. By applying the proposed method, faults can be quickly located, thus detection efficiency and detection accuracy are improved. Finally, a transformer winding ultrasonic synthetic aperture detection system is designed in this paper, and a 400 kHz ultrasonic transducer is used to conduct experiments on a transformer. The final experimental results show that the detection system can locate the deformation position of the transformer winding quickly online. The relative error of the detection is only 4.26%.