Pumping a single-mode, tunable, external-cavity laser to excite the whispering gallery modes (WGM) of micro ring resonators (MRRs), a series of equidistant, wide free spectrum range (FSR) can be observed. Frequency shift of FSR can be used to feedback external changes, making MRR very promising in high-sensitivity sensing. In this paper, a novel displacement sensor composed of a micro ring resonator and a waveguide is presented and a designing route for this sensor is discussed. Based on mathematical analysis and the beam propagation methods (BPM), the major parameters including the geometry of MRR and micro cantilever are investigated in detail. Materials selection and fabrication method under current processing technic are also presented. For the typical structure in this paper, the final Q factor is estimated approximately 103 in theory at the wavelength of 1.5μm.Displacement alteration of cantilever is 0.296x10-6m - 0.535x10-5m approximately corresponding 10-8-10-6N force loading. The shift of transmission spectrum is about 3.9nm versus perimeter of MRR changing 1μm.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.