A surface plasmon polaritons lithography model was presented based on thick metallic slit arrays to fabricate aperiodic nanostructures. The excitation of surface plasmon polaritons, model selection in thick metallic slit arrays and the intensity distribution in photoresist were studied carefully with finite-difference time-domain method. The results show that the diffusion of surface plasmon polaritons on slits can be inhibited, and the exposure depth is enhanced by optimizing the slits structure and matching medium lay. So periodic and aperiodic nanostructures are able to be produced by this technology. This may be helpful to fabricating nanostructures by laser direct writing technology.