Conform mesh technique is usually adopted to eliminate the step approximation error caused by the traditional Finite Difference Time Domain(FDTD) method. In this paper，the conformal mesh technique was introduced into the derivation of passive Maxwell's equations. To update the electric field iterative equation of the traditional Finite Difference Time Domain method，a linear weighted average method was used to obtain the equivalent conductivity of the edge electric field. Using the projection theory，the position coordinates of the conformal mesh were calculated，and then the conformal parameters of the target body were obtained. The electromagnetic responses of this method are consistent with that of the finite element method. Compared with the step approximation method，the conformal mesh technique shows a higher computational accuracy when calculating a three-dimensional anomaly with a curved surface. The more the electric field is required to be processed conformally，the more obvious the effect of the conformal mesh technique is，the accuracy is also improved greatly as a result. This method sets the fundamental to calculate complex underground anomalies of airborne electromagnetic.