Observation window structure of large mill protective cover

An observation window structure of a large mill protective cover relates to the technical field of mills and comprises a sealing door frame, a protective cover, an observation hole and a cover plate, the sealing door frame is fixed outside the observation hole in the protective cover, the cover plate connected through a rectangular flange is arranged on the upper portion of the sealing door frame, and an oil baffle plate is fixed on the inner surface of the cover plate. A locking base is fixed to at least one side face of the sealing door frame, a locking device arranged on the cover plate in a pressing mode is arranged on the locking base, each rectangular turned-over edge comprises a lower bottom plate and fixing plates extending upwards from the four edges of the lower bottom plate, the four edges of the bottom face of each rectangular turned-over edge are fixed to the upper edge of the sealing door frame, and n-shaped sealing strips are fixed to the upper edges of the rectangular turned-over edges. The ou