The invention relates to the technical field of generators, and discloses a stall cut-off protection device for a hydro-generator. The stall cut-off protection device comprises a shell, a water inlet pipe is fixedly connected in the shell, a direct illuminating lamp is fixedly connected in the shell, a photosensitive assembly is fixedly connected in the shell, a gear is rotatably connected in the shell, a toothed bar is slidably connected in the shell, a connecting rod is rotatably connected outside the toothed bar, and a rotating rod is rotatably connected to the end, away from the toothed bar, of the connecting rod. Through mutual cooperative use of the shell, the water inlet pipe, the direct illuminating lamp, the photosensitive assembly, the gear, the toothed bar, the connecting rod, the rotating rod, a sealing plate and a sleeve rod, after a water turbine stalls, through automatic operation of mechanisms, the effect of water turbine stalling automatic protection can be achieved, the situation of long-time overload operation of the water turbine is further avoided, internal accessories of the water turbine are protected, the service life of the water turbine is prolonged, and the manual maintenance cost is reduced.