Taking the patrol aircraft using the airborne MAD for example, the paper put forward a method of magnetic gradient to get the position of the submarine. On the base of analyzing the magnetic field characteristic of the submarine in detail and setting up the magnetic field model, how the patrol aircraft to make use of airborne MAD to survey submarine was analyzed and set up the model, and according to the characteristic of airborne MAD, the paper took far field magnetic signal be equivalent of magnetic dipole magnetic field. Result shows that through following and surveying 3 times that the position of submarine can be got accurately.