Based on the derjaguinmullertoporov(DMT) contact model, the interaction response of three typical tip cantilever and four materials samples with different mechanical properties during the tip sample approaching were studied in the amplitude modulated atomic force microscopy(AMAFM). It has been shown that the tipsample interaction force is strongly related to the phase of the first harmonic.Furthermore,we can easily determine the distance in which the tip will affect the sample with attractive and repulsive interaction forces from the amplitude modulated approach curves,which is helpful for optimizing the setpoint in the scanning process of the amplitudemodulation atomic force microscopy(AMAFM) imaging and avoiding the damage of the sample.