The hybrid systems that couple optical and mechanical degrees of freedom in nanoscale devices offer an unprecedented opportunity and development in laboratories worldwide. A nano-optomechanical (NOM) system that converts energy directly/inversely between optics and mechanics opens an approach to control the behavior of light and light-driven mechanics. An accurate measurement of the mechanical motion of a fiber-taper NOM system is a critical challenge. In this work, an optical microscope was used to measure the nanoscale mechanical motion of the fiber taper by introducing white light interference. The resolution of mechanical motion monitoring achieved 0.356 nm with an optomechanical efficiency of >20 nm/μW. This paper describes an approach to characterize NOM transducers between optical and mechanical signals in both classical and quantum fields.