The invention discloses a partial discharge ultrasonic detection and accurate positioning device and method for a transformer. A sounding method is applied to discharge detection of a transformer oil tank, a sounding probe is connected to a central controller and the like by a signal conversion channel plate, a path of sound signals when a first sound signal arrives are used for triggering remaining sound signals, a measuring system begins sampling, and the position of a discharge source is solved by measuring different propagation time of partial discharge sound signals arriving later and the geometrical position of a sensor. The device and the method for calculating, detecting and positioning the discharge source have the characteristics of high sensitivity, high accuracy and external interference resistance. Moreover, after the position coordinates of the discharge source are solved, a step of verifying the position coordinates is further provided in the solution, so that the detecting and positioning accuracy is further improved.