The utility model provides a self-driving combined probe for the ultrasonic flaw detection of a car axle. The probe comprises one than one sub probe, wherein, the sub probes are different in angle, and a wafer and a lead wire are arranged in each sub probe. The utility model is characterized in that the sub probes are evenly arranged on a probe turntable, an elastic positioning device is arranged in the central position of the probe turntable, a driving unit and a coder which are capable of rotating in phase with the probe turntable are arranged on the probe turntable, the center of the elastic positioning device serves as the rotation center of the probe turntable, and a magnetic positioning part capable of being connected with the car axle to be subject to the detection is arranged at the front part of the self-driving combined probe. The utility model has the advantages of simple operation, quick detection, good flaw detection performance and low possibility of missing or failing to judge. The elastic positioning device enables the utility model with great adaptation benefits to be quickly and accurately positioned on the end surface of the axle.