This paper presents two problems of calibration method for ultrasonic partial discharge detector: the method can’t reflect the pulse ultrasonic caused by partial discharge; the method can’t distinguish between the longitudinal wave and the surface wave when ultrasonic propagates in the medium. For problem one, this paper analyzes the frequency band through FFT, proposes to control ultrasonic source to give out pulse wave and envelope sine wave rather than continuous sine wave, and put forward the corresponding sensitivity experiment method. For problem two, this paper analyzes and calculates the transmission path of ultrasonic, choose specific cylindroid steel block (the bottom diameter of 600mm, height of 300mm) as experiment platform, and distinguish between the longitudinal wave and surface wave. In the end, experiment shows that the method in this paper can get the sensitivity curve and can effectively distinguish the types of ultrasonic in medium by sound velocity.