The invention belongs to the technical field of primary side overhaul equipment of a steam generator of a pressurized water reactor nuclear power station, and particularly discloses a primary side main connecting pipe high water level blocking board of the steam generator. The primary side main connecting pipe high water lever blocking board comprises two side boards and a central board. The central board is installed between the two side boards, the central board and the two side boards are matched to form a completely circular structure and each side board is provided with a detecting assembly. The central board and the two side boards are all embedded inside a sealing assembly. The side boards are fixedly installed on a primary side main connecting pipe through double-threaded screw assemblies. The double-threaded screw assemblies are installed on the main connecting pipe through bosses. The central board is fixedly installed on the main connecting pipe through a locating pin. The blocking board can be used for conducting sealing on a primary side water chamber of the steam generator before high water level arrives and the time needed in the overhaul process is guaranteed.