On the basis of the past practice on the application, the purpose of this paper is to study the anomaly genesis of the frequency selection method for a sphere in homogeneous half space. First of all, from two aspects of natural factors and human factors analyse the natural electric field method of frequency selective source problem. Based on the Maxwell equations and the boundary conditions, the analytic expressions of an induced electric field outside the conductive magnetic sphere are obtained for a sphere under harmonic magnetic field in homogeneous half space. According to Laplace equations and boundary conditions, the horizontal component of anomaly field on the surface is obtained for a conductive sphere under harmonic electric field in homogeneous half space. Parameters of models are assumed, profile curves of total electric field on the ground are calculated for a conductive sphere under three dimensional harmonic electromagnetic fields. Theoretical simulating curves are compared with the practical exploration curves, and similar characteristics are indicated when the sphere under horizontal harmonic magnetic fields and stray electric fields in homogeneous half space.