Abstract: To understand distribution characteristics of electromagnetic field in the building under near- and far-field radiation by narrow band electromagnetic pulse, computation results of multiple-storey multi-unit building under oblique incidence of plane and spherical electromagnetic waves are comparatively analyzed by finite-difference time-domain(FDTD) method. The electrical field amplitude at centers of different altitude planes in room and the maximum distribution of electrical field strength at different altitude planes in building are generally analyzed. The field distribution of corresponding altitude planes on each floor in building is similar. The field strength of areas where the incident wave propagates from windows into rooms is stronger, and is identical under the incidence of both kinds of electromagnetic waves. The field strength of the rest areas in wider space under incidence of spherical wave is weaker than that under incidence of plane wave. By used of the field source with spherical electromagnetic wave closely fitting the building form, the spherical wave of narrow band propagating in empty space is simulated, and computation results prove the field source of spherical wave constructed accurately workable.