The measurement of large-size components needs a larger measurement range, while the high-precision scanning sensor has a small field of view in most cases. In order to solve this contradiction, a structured light scanning measurement method based on mechanical splicing was proposed. The partial high-precision point cloud was obtained by structured light scanner and the data splicing was realized by high-precision cross translation platform. Firstly, the composition and measurement principle of the system were analyzed, and an external parameter calibration method based on weighted nonlinear optimization was proposed to solve the transformation relationship of the intangible coordinates between the structured light scanner and the cross translation platform. Finally, it was verified in the experiment that the root-mean-square error (RMSE) of sphere-center distance was better than 45 μm within the measurement range of 300 mm. And the feasibility of the proposed measurement system was verified by measuring the physical components.