An optimization method and its derived solution for uniform lighting source of a metal linear test object with high curvature in space are proposed to solve the gray-scale image display problem attributed to the wide variations in brightness on the surface of the metal linear test object caused by uneven illumination in visual inspection. First, the ideal lighting model of any point in the lighting space is established using photometric theory. The mathematical relationship between the surface illuminance, reflectance, spatial coordinate information, and image gray level of the point is then derived, and the simulation is performed using MATLAB. Analyzing the data yielded the primary factors influencing uniform illumination and imaging of the measured object. On this premise, the dome light source is utilized to improve the illumination light source, and the surface uniformity of the metal linear measured object is 92.85%. The experimental findings demonstrate that this technique can effectively improve the surface uniformity of the metal linear object, up to 34.77% higher. Furthermore, it can effectively solve the imaging problem during visual inspection of this type of object.