The isograms of scalar Green's function in EM theory near singularity are discussed,including several bounded and unbounded 2-D and 3-D Green's function.The result shows that near singularity,the isogram of 2-D Green's function trends to circle,and 3-D Green's function trends to sphere regardless of the type of boundary.Whatever complex the bounded Green's function is,they have all same properties with unbounded Green's function.This is very useful to regularity process of integrative equation in EM field calaculation.