A algorithm based on the iterative method was presented with Finite-Difference Time-Domain (FDTD) arithmetic. The main principle is that the unknown field for the current iteration is replaced approximately by the field produced in previous iteration with the time-stepping method. The difference between approximated and real fields decreases with the increase of iterations. Specific procedure of the algorithm was discussed and the convergence analysis was presented. By calculating the reflection coefficient of infinite gold plate and compare it with analytical solutions,it is concluded that the two results are highly consistent with each other numerically and this algorithm turns out to be right. The transmission of three-dimensional dispersive structure with nano cylindrical structure on silicon surface is simulated to verify this method. Results clearly show that this method overcomes the limitation of incidence angle,lack of time domain field evolution procession and need for large meshes compared with traditional methods,which provide a new solution for transmission properties of dispersive periodic structures under oblique incidence conditions.