In this paper, a magnetic inductive head probe is used to detect micro-cracks in bearings. For the width of the crack in bearings is less than 15μm and the leakage filed is so weak, a flexible probe system is designed to keep the magnetic inductive head probe fit with the bearing surface closely. Micro cracks in a magnetic particle testing block are detected with the magnetic inductive head probe. The limit detecting crack size of magnetic particle inspection (MPI) is calculated by Boltzmann distribution function. Magnetic inductive head has a higher sensitivity than MPT in bearing parts inspection system.