The invention relates to the technical field of partial discharge detection, in particular to a test device used for measuring ultrasonic partial discharge signal attenuation in an ultrasonic method. The test device comprises a high-voltage lead terminal, a horizontal bus sleeve and a vertical bus sleeve, a horizontal high-voltage conductor is arranged in the horizontal bus sleeve, a vertical high-voltage conductor is arranged in the vertical bus sleeve, the high-voltage lead terminal is connected with the horizontal high-voltage conductor, the vertical high-voltage conductor is connected with the horizontal high-voltage conductor through an isolation switch, the connection portion of the isolation switch and the vertical high-voltage conductor is of an L-type structure, the portion of the L-type structure between the high-voltage lead terminal and the horizontal high-voltage conductor is provided with a discharge pointed end, ultrasonic sensors are arranged in the horizontal bus sleeve, on the isolation switch and in the vertical bus sleeve respectively, and the ultrasonic sensors are all connected with an oscilloscope through coaxial cables identical in length. The test device can provide a theoretical basis for best installation positions and the number of the ultrasonic sensors in a partial discharge online monitoring system.