A rigorous vector analysis model based on body-of-revolution (BOR) finite-difference time-domain (FDTD) method is presented, many design examples of multilevel circular microlens are analyzed by this model, and the influence of design parameters and fabrication error on the focusing performance of the designed microlens is investigated. The results show that the electric field magnitude on focus increases, and the focal radius and focal depth minish when the zone number is increased but other parameters such as focal length and incident wavelength are constant. The focusing effect is intensified when adding step number only, but after the step number adds to 8～10, the focusing effect tends to be stable. It's suggested that the step number is set as 8～10 in actual fabrication. When binary mask is used to lithograph the multilevel, fabrication error is easily generated. Two kinds of multilevel microlens with alignment error or system etching error are designed, which generate the above error in the third etching process of fabricating eight levels. Analysis result shows that the alignment error has passive influence on the focusing effect of multilevel microlens, so it should be avoided in fabrication, but the system etching error has little influence on the focusing effect of multilevel microlens.