The invention relates to a micrometric displacement sensor based on an integrated planar ring-shaped micro cavity and a cantilever beam, which comprises a planar ring-shaped micro cavity, an optical waveguide, a substrate, an incidence fiber connected with the optical waveguide and an emergence fiber connected with the optical waveguide. The planar ring-shaped micro cavity is coupled with the optical phase of the optical waveguide. The micrometric displacement sensor is characterized in that the micrometric displacement sensor also comprises a cantilever beam and a probe; one end of the cantilever beam is connected with the substrate and the other end of the cantilever beam is a free end; the probe is positioned in the middle of the front part of the free end on the lower surface of the cantilever beam, and both the cantilever beam and the probe are formed by etching; and both the planar ring-shaped micro cavity and the optical waveguide are etched on the upper surface of the cantilever beam. The micrometric displacement sensor is made by using a modern MEMS processing technology, can be used in complex magnetic field environments, vacuum environments, can be used for measuring wide range of objects, including the measurement on the surfaces of biological cells as well as the surfaces of metals and non-metals, and has the measuring precision of 10<-4> angstroms.