The designing formula of multilevel diffractive microlenses is presented. Body-of-revolutionary finite-difference time-domain method (BOR FDTD) is illustrated. The multilevel diffractive microlenses are analyzed by use of BOR FDTD. The effects of changing design parameters (including focal length, incident wavelength, refractive index of microlens material) on multilevel diffractive microlens are investigated. The results show that changing design parameters have effects on diffractive efficiency, airy diffraction disc radius and maximum electric magnitude of microlens. The qualitative analyses of microlenses are consistence with some of numerical results.