Silver superlens has a great influence on super-resolution lithography, imaging and the biosensing based on surface plasmon polaritons. In this paper, the surface plasmon resonance and the imaging of silver film are discussed in detail with optical transfer function of silver superlens. And the imaging process of silver superlens has also been simulated with the finite difference time domain. The simulation results are in agreement with those from the theoretical formulas, which fully proves the optical transfer function to be reliable. This may be an effective method of rapid parameter optimization for sensors, super-resolution imaging and enhance the interference lithography based on surface plasmon polaritons.