Abstract: The principle is presented and demonstrated of using a single He-Ne laser to sense displacement without nonlinear error in principle,and with function of self-calibration. By using frequency-splitting technology,we could separate a mode interval into four equal-width ranges with different intensity characteristics. One cavity mirror of the laser moves λ/8 along the laser axis when a laser frequency crosses one such range. The moving mirror contacts with and is moved by the object to be measured. Thus the He-Ne laser becomes a displacement sensor without using interference phenomenon which works with accuracy of 0.079μm,10mm measuring range,and function of distinguishing direction.