In the optical lithography technique, the higher aspect ratio is critical as well as small spot size. To achieve higher aspect ratio with the same nano scale spot size, in this report, we control the confocal parameters of Ag superlens by changing the position of lens. In our FDTD (Finite Difference Time Domain) calculation, Drude dispersion is employed to represent the frequency-dependent permittivity of the Ag superlens while the refractive index of Ag matches with the host material, air and PMMA, at the wavelength of 338nm and 360nm. By changing the wavelength from 330nm to 340nm, in addition, we investigated the tunable superlensing effects and the amplification of evanescent wave with Ag slab related to surface plasmon polariton. Consequently, we observed the variation of the confocal parameters of Ag superlens depending on the position and the tunable wavelength in our results.