In the line structured light three-dimensional measurement system, the high-precision laser stripe center-line extraction is the key to improve the measurement accuracy. Aiming at the existing laser center-line problems such as low extraction accuracy and poor retention of details, a laser center-line extraction algorithm based on normal guidance was proposed. The specific implementation steps of the algorithm were as follows: Firstly, the image was pre-processed, and the laser line was preliminarily extracted by combining edge detection and geometric center method. Then, the principal component analysis (PCA) was used to obtain its normal line, divided the angle eight neighborhood at the laser center point, and searched for the effective point set through the normal angle guidance. Finally, the gray centroid method was used to extract the sub-pixels from the point set. The experimental results show that the root mean square error of the algorithm is improved by 0.233 9 pixel compared with that of the gray centroid method, which can retain the light strip details better than the Steger algorithm and the directional template method, and can extract the light strip center more accurately and achieve the sub-pixel level accuracy.