The utility model discloses a transformer partial discharge ultrasonic detection and fine positioning device connects sounding probe and the central controller who sets up on the oil tank lateral wall through the signal conversion channel board, and the signal conversion channel board is including the preamplifier, sampling holder, AD converter and the high -speed memory that cushions that connect gradually. Be applied to transformer tank's discharge detection with the sounding method, connect the sounding probe in parts such as central controller through the signal conversion channel board. The utility model discloses a device has clever lightness height, the degree of accuracy is high, and its testing process and result do not receive external disturbance's characteristics.