The embodiment of the invention discloses an automatic switching device of ultrasonic signal channels, which comprises a control module, an ultrasonic electronic module and an ultrasonic channel switching module. The automatic switching device of the ultrasonic signal channels is characterized in that: when online detection is carried out on wheels of a locomotive, the control module sends external triggering information generated by movement of the wheels to the ultrasonic electronic module, and then the ultrasonic electronic module generates an exciting signal for exciting an ultrasonic wave probe to work. Meanwhile, the control module sends channel switching information to the ultrasonic channel switching module, so that the ultrasonic channel switching module conducts the needed ultrasonic channel, and the exciting signal sent by the ultrasonic electronic module and a received probe echo signal realize detection by the conducted ultrasonic channel. The ultrasonic channel switching module automatically switches numbered ultrasonic electronic channels on the ultrasonic electronic module, thereby realizing connection of fewer ultrasonic electronic channels with lots of ultrasonic wave probes, accomplishing automatic detection of the whole wheels, and saving cost.