To study the impact of reflector shape on the performance of a reflective intensity-modulated fiber optical distance sensor with single mode illumination, a theoretical model was established based on the assumption that the single mode fiber output light field is the modified approximate Gaussian distribution. By introducing the reflector shape factor, the influence discipline of the reflector shape factor on the intensity modulation characteristics was analyzed. Simulation results indicate that for concave reflector, as the radius of curvature increases, the sensitivity of the back slope becomes larger and the linear range of the back slope becomes smaller while those of the front slope remain almost unchanged. However, for convex reflector, as the radius of curvature increases, the sensitivity of the back slope becomes smaller and the linear range of the back slope becomes larger while those of the front slope also remain almost unchanged. As the radius of curvature increases, the effect of the nonplanar reflector becomes weaker until it disappears.