A rigorous vector analysis of diffractive optical elements(DOEs) that are finite in extent and have subwavelength structures was presented by using a two dimensional finite-difference time-domain(FDTD) method.The focusing characteristics of continuous profile lenses and subwavelength lenses(SWLs) obtained by generalizing the design approach presented by Farn,for different incidence polarization waves (TE polarization and TM polarization) and for different F-numbers of lenses were analyzed.The comparative results have shown that the focusing characteristic of SWLs is more sensitive to the polarization of incidence wave than that of continuous profile lenses.Minimizing the numerical dispersion in the FDTD calculation region and setting the absorbing boundary have been discussed also.