This invention discloses a three-dimensional B ultrasonic device for disk scanning. In the three-dimensional B ultrasonic device, a thrust ball bearing 1, one end of an outer sleeve, a thrust ball bearing 2 and a nut are connected sequentially and are fixed on the outer wall of the inner layer of a shell; a motor 1 passes through the inner layer of the shell and is connected with a photoelectric encoder 1 and a coupling sheet 1 sequentially; both ends of a transmission bar are connected with the coupling sheet 1 and the outer sleeve respectively; the other end of the outer sleeve is fixed on a supporting sheet; one end of a motor fixing sleeve is connected with the supporting sheet; a motor 2 passes through the motor fixing sleeve and is connected with a coupling sheet 2; a photoelectric encoder 2 is arranged between the motor 2 and the coupling sheet 2; an ultrasonic sensor is fixed on the coupling sheet 2 and is connected with a control line board; the control line board is connected with a programming controller and is used for regulating and controlling the rotation speed of the motor 1 and the motor 2; and the outer layer of the shell is used for accommodating the thrust ball bearing 1, the outer sleeve, the thrust ball bearing 2, the motor 1, the coupling sheet 1, the transmission bar and the photoelectric encoder 1. The three-dimensional B ultrasonic device has a simple structure, a controllable scanning range and high scanning efficiency and is convenient to operate and simple in data processing.