Abstract: Geomagnetism Aided Navigation （GAN） is a new branch of the integrated navigation technique. Navigation principle and the development of the GAN system are introduced in the paper. The emphasis is laid on the research of the matching method. Geomagnetic matching is the technique that uses a geomagnetic map to determine the location of the vehicle. The obtained position information can be used to limit error accumulation of the Inertial Navigation System （INS）. An improved correlation matching method based on the contour constraint is proposed. Map contour is used to confine the searching process, changing the uncertainty field to an uncertainty line, which efficiently reduces the computation burden of the system and eliminates the initial position error of INS. A nearest point principle （NPP） is applied in the precision matching part. The NPP technique can bind the error of INS accumulated during the matching process. The simulation results show that the proposed method can greatly improve the efficiency and precision of the whole GAN system. The accuracy of the matching method is less than the unit cell size of the map. In addition, the proposed method is, to some extend, adaptive to the heading error of the INS.