A static numerical simulation model of a U-shaped ACFM inducer is built to observe the distribution of current density and magnetic field near the crack, and a dynamic model is developed from it to model a real ACFM probe passing above a real specimen with a crack. The dynamic model is verified by comparison with experimental data and shows good agreement. The influence of various parameters, such as material and dimensions of core and inducer lift-off on the perturbed magnetic field above the crack is modeled and discussed. The suggested parameters are given for the design of the inducer according to the influence analysis results. The numerical simulation results will provide guidance to the design of the U-shaped ACFM inducer.