This study constructs a novel scanning near-field optical microscope (SNOM) fixed-amplitude simulative measuring model. It uses Al, Si, and O atoms to compose the probe tip and sample to construct the atomic model of SNOM simulative measuring model. It also applies Morse potential to calculate the atomic interaction force between tip and sample on the vibration theory of SNOM. This study compares the edge effect of surface profile between the simulated measurement with experimental measurement; it verifies that the nanoscale simulative measuring model for SNOM is reasonable and accurate. After analyzing the edge effect and error about the surface profile of standard sample by the SNOM simulated measurement, it is found that the factor influencing this surface profile appearance is mainly from the tip shapes. The investigation of the error analysis is referential in compensating the error of SNOM measurement and it can be used to further enhance the accuracy of SNOM measurement.