Abstract: In geology and mineral resources survey and geophysical exploration,high-precision magnetic measurement is characterized by economic,practical,and fast,so it find a wide application in searching for ferromagnetic minerals and geological structures.However,in data pre-processing,the corroction of normal field gradient is relatively complicated and has a bigerror.Through comparison between practical examples,we point out the problem exists in current norms of normal magnetic field gradient measurements to correct the problems,discuss the correction of the normal field gradient method,and propose a new method for the correction.In addition,we also put forward a calculating method which is fast in calculation,making the pre-processing of magnetic measurement data become more simple and accurate.