Abstract: Calculating eddy currents in oil-well casing pipe requires numerical methods to solve Bessel equations. The finite difference method for analyzing static fields is used to analyze sinusoidal steady-state field by using phasor method. Differential equations for solving electric field intensity are turned into those for solving magnetic field intensity. This turns the second-class boundary problem into a first class one and makes the solving process more easy. The method is also suitable for other axis-symmetrical fields.