In three-dimensional testing systems based on line structured-light,due to the effect of the line structured-light quality and the nonuniform of object surface reflectivity as well as the surface roughness,the laser stripe often appears some problems such as the uneven width,non-concentrated brightness and larger discreteness. An improved gray centroid method to extract the center line of laser strip was proposed. Based on the adaptive binarization processing,the normal widths of each column and accurate edge of the light stripe were obtained. Then,according to light stripe’s edge and gray data,the center of light stripe was calculated by the gray centroid method. The results prove that the calculated range of centroid in the improved method is consistent with light strip width,so it has high extraction accuracy and good adaptability.