Abstract: Optimization design of ACFM inducer is performed by using ACFM experimental platform. The U-shaped core is used to induce magnetic field, and the core material, core structure, induction coil structure and induction voltage is considered to achieve the optimized design of ACFM inducer. By numerous experiments, testing of 4 dimensions of typical defects is performed to verify the testing effect of the optimized ACFM inducer. The results show that the resolution of the carck detection reaches to 3 mm.