The rod-anode X-ray source can stick into an object for nondestructive inspection, which is preferred for reliability inspection of the metal tube wall parts with of small cavity. A focusing system with a good electron-optical design is one of the keys to the high-resolution inspection of rod-anode X-ray sources. The focusing system is modeled in terms of the electron-optical theory and the structural characteristics of the rod-anode X-ray source. The electron-optical parameters of this model are then optimized, and the prototype is built for the resolution tests. Both the simulation and experimental results indicate that the resolution of the prototype is better than 50 μm under the acceleration voltage of 50-130 kV.