The invention belongs to the technical field of nuclear power maintenance and particularly relates to a mounting and fixing device of a nuclear power station water discharging port flashboard guide groove auxiliary anode. In the embodiment of the invention, a placing cylinder is connected with a pedestal; the pedestal can fix the placing cylinder, in which the auxiliary anode is placed, at the bottom end of a water body in water flow of the water discharging port, so that impact on the auxiliary anode and a cable by sea water can be effectively reduced and the fact that the auxiliary anode isthrust and washed away is avoided; in addition, a hollow structure of the side wall of the placing cylinder enables the auxiliary anode to be completely contacted with the sea water, the protective efficacy of a cathode protective system is enhanced and impact on the placing cylinder by the sea water can be reduced, so that the auxiliary anode can exert effect stably, has longer service life and reduces manual maintenance risk and cost.