A new method to test the optical performance of a medical rigid endoscope was proposed to inspect its quality. First, the mesh maps of images were transformed and qualitatively observed and judged by a quality testing device. Then, the images were treated using gray-scale transformation and binarization to find the chord-line passing through the center and to draw up plot curves. By fitting analysis of plot curves, the horizontal and vertical ratio of edge and center and the FOV difference in brightness ratio were both calculated. Obtained data were analyzed and experiments on the domestic and overseas medical rigid endoscopes were performed. The results indicate that the FOV difference in brightness ratio of domestic endoscopes has a good correlation in horizontal and vertical directions, their values are all above 0.908 5 and the correlation is independent on the brightness. The imported endoscopes have a better relevance ratio of edge and center in horizontal and vertical directions and their values are above 0.656 5. Moreover, FOV difference in brightness ratio is proportional to brightness, and the ratio of edge and center is stable. It concludes that the chord-line method is able to calculate the FOV difference in brightness ratio and also shows the performance evaluation vividly. This new method is simple and convenient, and suitable for test and evaluation of the light efficiency performance of medical rigid endoscopes.