In this paper, we present performance optimization for a home-built scattering-type scanning near-field optical microscope. We studied the influence of both the vibration amplitude and the amplitude setpoint of scattering tip on background suppression and near-field signal extraction. It’s demonstrated that the amplitude of small vibration similar to the size of tip climax is beneficial to suppress background related to far-field scattering from probe shaft and cantilever. In order to reduce the influence of vibration harmonics on signal demodulation during probe scanning, the ratio of feedback amplitude setpoint to free space vibration amplitude must be 90% at least.