Intensity for the research on the fiber end and send a Gaussian beam in the reflective surface under the premise of specular reflection and diffuse reflection, through the theoretical analysis of the establishment of a reflective intensity modulation optical fiber sensor function model is established. By the use of Matlab, the reflective surface roughness change and the parameters on fiber itself are analyzed. The effects of smooth mirror and completely diffuse reflector on the modulation characteristics and the effects of optical fiber on the axis spacing, core radius and numerical aperture of optical fiber on the modulation characteristics are studied. The results show that the intensity modulation characteristic of specular reflection is obviously better than that of diffuse reflection, and the peak value of modulation function is 5 times of that of diffuse reflection. In terms of the design of fiber sensor, the optical stress characteristics and measurement accuracy of the fiber sensor can be improved by reducing the spacing between the transmitting and receiving fiber axes, reducing the sending fiber core diameter, increasing the receiving fiber core diameter, and selecting the fiber with larger numerical aperture.