The generator vibration of the unit is sensitive to the running conditions for the low-head turbine group's low head, high flow characteristics. The generator local stress concentration often leads to fatigue rupture of the metal structure, which will also affect its reliability. It easily leads the generator bracket of oblique arm structure to cracking and rupture. The reason of the cracking and rupture is proved by numerical analysis, and its repair plan has been identified. On-site repair process should be strictly controlled, to ensure the greatest degree of welding quality and the elimination of welding stresses. Running for some time after repair, the main parameters, such as air-gap and other unit operation, have been analyzed. The results are satisfying, and confirm that, the analysis of the generator bracket crack repair is objective and reasonable.