The invention discloses a transformer internal partial discharge determination device and a positioning method thereof, and solves the problems that existing transformer partial discharge determination is big in error and low in performance cost; the top of a cylinder sensor mount (4) is provided with 7 ultrasonic sensor plug slots (5) and ultrasonic sensors (6) arranged in an L-shape; a spring (7) is arranged between the bottom of a cylinder groove (3) and the bottom of the cylinder sensor mount (4); an ultrasonic signal leading-out wire (8) of the ultrasonic sensor (6) is electrically connected with an ultrasonic data collector (9) through a through hole (11); the ultrasonic data collector (9) is connected with a computer (10); L-shape array sensors are employed, a wideband focusing algorithm of a total least spuares (TLS) is used for focusing partial discharge ultrasonic broadband signals, and a narrowband direction finding algorithm combining a phase match principle with cloud optimization search is used for obtaining orientation information of a partial discharge source. The transformer internal partial discharge determination device is high in direction finding precision, and accurate in positioning.