Abstract: At present, the acceleration sensor widely used in inertial navigation system of aviation industry can′t offer effective immunity towards the electro magnetic interference (EMI) and electro magnetic pulse (EMP), so a novel optical acceleration sensor based on a Fresnel diffractive microlens is proposed, which can solve the problems mentioned above effectively. The sensing principle of the sensor is that a reflecting membrane is put behind the microlens in parallel, and the acceleration is calculated by measuring the variation of the light intensity at the converging point in front of the microlens. The optical principle of the sensor is discussed in details by using Fresnel-Kirchhoff diffractive formula. The effect of the optical fiber deviation on the light intensity is analyzed with the computer simulation. The results prove that the light intensity received by the optical fiber has visible changes even for the nanometer level changes of the position of the reflecting membrane and is highly sensitive to the deviation of optical fiber in the direction of the focal plane. The light intensity will drop off to less than 50% of ideal light intensity when the deviation exceeds 2 microns. Moreover, the principle of this sensor was proved to be correct by a demonstration experiment.