Abstract: The numerical solution of an electic dipole on a layered medium is materially Hankel-transform.By working three models of numerical solutions,which explain how the electromagnetic fields are effected by the Hankel transformation coefficient,then we know adding filtering factor can increase computation precision apparently and make the result of forward solution reflect actual situation reliably;otherwise,if the filtering range is too short the field data and apparenty resistivity may be impacted largely.Therefore,select correct filtering factor can improve the computation precision and computation speed.