Abstract: For its advantage of non-contact detection, electromagnetic nondestructive testing is feasible to achieve high-speed online rail crack inspection, but the velocity effects caused by the rapid relative motion between the detection probe and the measured rail have a strong impact on inspection results. In this paper, starting from the basic principles of electromagnetic field, the effect of velocity on High-speed Magnetic Flux Leakage Testing was analyzed and some methods of high-speed online rail crack inspection were proposed according to the characteristics of the speed factor. It was concluded that the best test results could be achieved by longitudinally and transversely magnetizing the rail surface with the DC excitation yoke, and the detection probes being with 3D-hall sensors & 3D-coils located in the middle of the yoke magnetic poles and the detection coils being wrapped around the arm of the yoke. The experimental results from the platform of high-speed non-destructive testing showed that the proposed inspection methods could effectively achieve high-speed online rail crack inspection, and different methods had their own respective advantages to identify the different types of rail cracks, methods complementing each other could achieve high-speed online inspection of the different types of rail cracks and effective identification of defects above 200 km/h.