A superlens which can work at visible wavelength and whose work wavelength can be manipulated is proposed. It consists of a plasmonic metal film layer and two dielectric film layers. The relationship between the dielectric layer and the surface plasmon waveguide mode is analyzed, and its sub-wavelength imaging law is given. The results show that a sub-wavelength image with high transmittance and resolution of λ/6 can be obtained in the range of 365~515 nm. The fabrication tolerance and surface roughness can be greatly reduced, ascribed to its quite simple structure. Its simple structure and excellent sub-wavelength imaging capability opens a door for potential applications, such as sub-wavelength lithography, bio-microscopy and high intensity storage.