Photolithography resolution could be enhanced by the local enhancement effects of surface plasmon polaritons (SPP). Large-area periodic nanostructures could be fabricated by backside exposure SPP interference lithography. Resonance transmission of SPP in backside exposure system is analyzed, an optimum design method is proposed for silver superlens, and the intensity distribution of SPP interference lithography is simulated by finite difference time domain (FDTD) method and theoretic formulas. With optimum design of superlens thickness and resonance angle, a periodic silt array is obtained with better quality in laboratory.