During the forward transformation of wave-field, two-step optimized algorithm is used for decreasing the number of integral coefficients and sampling in dispersed digital integral, as while as ensure transient electromagnetic fields calculation precision.This algorithm solves the ill-posed problem produced by large quantity of integral coefficients and depresses the ill character of the first calculation function.During wave-field inverse transformation, normalized algorithm is introduced to the inverse transformation by adopting the deviation theory and the Newton iterative form to make the transformed wave field stable and reliable.It is concluded that this algorithm is effective and useful.