The measurement of laser displacement sensor is based on the scattering effect of the surface, and the roughness characteristics of the target surface directly affects the light intensity of the scattering measurement spot. For the purpose of studying the impact of the roughened surface on the light intensity of the imaging spot, the scattering geometry model of rough surface is built. By using Kirchhoff scalar scattering analytical theory and combining shadowing function statistical model, the functional relationship between the characteristic of the rough surface and the scattering luminous flux is calculated. According to the detection principle of the position sensitive detector (PSD) in the sensor, the light intensity value of imaging spot on the photosensitive surface will directly affect the measurement accuracy of the sensor. Through the analysis of the measurement data of different standard roughness surfaces which are got from the displacement sensor based on PSD, the experimental results show that different surface roughnesses will produce different measurement errors, and when the Rq value of surface roughness is larger, the light intensity of scattering spot becomes larger. But accompanied by significant enhancement of the shadowing coefficient, the light intensity is gradually weakened, and the magnitude of measuring error has the same trend of changes with that of light intensity. For the roughened surface with Rq=0.8 μm the measurement error is the minimum.