The invention discloses a gear protective cover of a large-scale mining mill. The gear protective cover is arranged outside a big gear and a small gear of a mill and comprises a top cover, a bottom cover and a small gear cover. Two ends of the top cover are respectively fixedly connected to one end of the small gear cover and the other end of the small gear cover is fixedly connected respectively to two ends of the bottom cover. A lower end of the bottom cover is provided with a support. The small gear cover comprises an upper cover, a middle cover, a lower cover and a cover plate. The upper cover, the lower cover and the middle cover are located respectively above, below and outside the small gear. A lower end of the upper cover and an upper end of the lower cover are fixedly connected respectively to an upper end and a lower end of the middle cover. Side walls of the upper cover, the middle cover and the lower cover at the same side form a gap corresponding to an engaged part of the big gear and the small gear. The cover plate is covered on the gas and fixed to the upper cover, the middle cover and the lower cover respectively by bolts. The gear protective cover can greatly reduce on-site installation and dismounting time and is convenient for fast detection of a tooth side gap of a big gear and a small gear.