With the development of semiconductor technology, improving precision of linewidth measurement allows of no delay. Measured with atomic force microscope (AFM), linewidth uncertainty is affected most by its tip. The effect on linewidth measurement by vibrating tip top's track and lateral profile of carbon nanotube tip (CNT) is illuminated by simulation. The track is described by vibration model. The profile is drawn-out from the tip’s lateral image photographed by scanning electron microscope (SEM). According to the simulation results, the essential conditions that linewidth is measured with CNT are presented. Improving parameters of cantilever can decrease or eliminate the effect of track.