Based on the established simple model of an optical system, the traditional readout signal of super-resolution near-field structure (Super-RENS) disc is simulated according to scalar diffraction theory and angular spectrum method. By comparing simulation results with experimental signals, the validity of the calculation method is proved. Moreover, the differential signal, which is the difference of signals read out by high and low power incident laser, is simulated for single track and three tracks recording pattern. It is shown that, by using the differential readout method, the cross talk from adjacent pits is decreased and high quality readout signal can be obtained.