Abstract: A new kind of industry ultrasonic probe, whose reflecting angle can be modified automatically and continuously, is proposed, and it is equipped with a micromotor. It can fulfill the cross sectional scanning to steel butt-joint welding seam detection in the good place by modifying the value K of probe and the value K of probe is changed by the micromotor driving. And the probe is moved along the straight line in good welding seam place, the whole welding seam can be scanned perfectly(namely coarse detection).