The invention discloses a containment vessel air cooling system for a million-kilowatt level nuclear reactor. The containment vessel air cooling system comprises a fan and an air duct, wherein an access hole is formed on the air duct and is provided with a cover plate used for plugging the access hole; the top surface of the cover plate is fixedly provided with a cover plate compressing piece; the cover plate compressing piece is detachably connected to the air duct in a rotating manner through a rotating mechanism and is detachably locked with the air duct through a locking mechanism which is arranged at interval to the rotating mechanism, so that the cover plate is fixed on the access hole in a sealing manner. Aiming at the defect that the cover plate in the prior art is fixed by adopting a great number of bolts and is inconvenient to disassemble, so that disassembly personnel are radiated by control rods for a long time, and the body health is influenced, the invention provides the containment vessel air cooling system for the million-kilowatt level nuclear reactor, which is easy and fast to disassemble and has good sealing performance.