The corresponding mathematic model was established to analysis the effect of obliquity of reflector on the light intensity modulation function of three fiber displacement sensor with intensity compensation. The simulation results of the RIM FOS characteristic parameters with the different obliquity of the reflector were computed and the characteristic curves were plotted. Results showed that in the fiber pair, with the increasing of reflection angle, the initial distance and the peak distance increased slightly; characteristic parameters of the peak point decreased obviously; the front slope of the curves changed slowly and the sensitivity decreased obviously. In the structure of three optical fiber, with the increasing of reflection angle, the initial distance and the peak distance increased obviously; characteristic parameters of the peak point did not change; front slope of the curves changed slowly and the sensitivity decreased slightly. The obliquity of the reflector exerted great influence on the modulation function of the RIM FOS, compared with the fiber pair, three fiber displacement sensor could improve the influence on the sensitivity of the modulation function induced by the obliquity of reflector to some extent, and eliminate the decrease of characteristic parameters of the peak point.