A rain cover for a main-transformer bushing comprises an inverted-T-shaped binding screw rod, a nut and a stainless steel cover. The binding screw rod comprises a round base plate and a screw rod body fixed in the middle of the round base plate. A threaded blind hole extending into the screw rod body is formed in the middle of the base plate of the binding screw rod, and is matched with a binding post on the main-transformer bushing. A seal ring is arranged along the edge of the upper surface of the base plate. An open hole is formed in the middle of the top of the stainless steel cover. The screw rod body of the binding screw rod penetrates the open hole. The stainless steel cover covers the base plate of the binding screw rod. The nut sleeves the screw rod body to lock the stainless steel cover, and the stainless steel cover and the base plate are sealed through the seal ring. The rain cover can prevent damp air and moisture from entering the bushing from an oil injection hole in the top of the main-transformer bushing effectively when being mounted on the main-transformer bushing, so that faults of the bushing and a main transformer are reduced.