Abstract: Aiming at detecting microcrack of the cam surface, the differential eddy current sensor was designed and made up by race track coils. And the COMSOL software was used to simulate and analyze the influence of coil spacing, lift-off, and curvature radius of the convex surface on crack signals. Then the optimal differential eddy current sensor parameters were obtained. According to the characteristics of the cam profile, the three-degree-of-freedom self-following structure was designed, and a flaw detection platform based on this structure to evaluate the detection performance was established. Finally, in order to meet the large-volume, high-speed and high-precision testing requirements in real industry, the whole camshaft automatic eddy current detection system was designed, and meanwhile a high-speed and high-precision automatic detection process was developed, in which the detection speed is 30 s/piece and the minimum detection depth is 0.1 mm.