Abstract: Optical feedback self-mixing interferometry is an emerging sensing and measurement technique,which is quite different with traditional double-beam interferometry.To perform precision displacement measurement under the condition of moderate optical feedback,a displacement measurement method was proposed based on moderate optical feedback self-mixing interference.Firstly,rough measurement of displacement was carried out by counting the fringe numbers with the resolution of half wavelength.Then based on the study of fractional fringe structure details,a measurement means for displacement within half wavelength was derived.Calibration results with a commercial piezoelectric ceramics which translates in the order of 3nm show that a displacement accuracy of nanometers scale is achieved in the common laboratorial environment.The results indicate the relative standard deviation of bΔL is 1.20% within the displacement less than 3μm.