The invention discloses a slag extractor used for subway construction. The slag extractor comprises a crane span structure, carts are arranged on the bottoms of the two ends of the crane span structure, a trolley is arranged on the crane span structure, an electric hoist is arranged is arranged on the trolley, a hopper is hung on a lifting hook of the electric hoist, a tipping device used for tipping the hopper is arranged on the trolley and comprises a first telescopic rod, an L-shaped connecting rod, a supporting device, a vertical connecting rod and a hook, the first telescopic rod is arranged in an inclined manner, the L-shaped connecting rod is hinged to the supporting device, the supporting device is fixedly connected with the trolley, the first telescopic rod is connected with the vertical connecting rod through the L-shaped connecting rod, the vertical connecting rod is fixedly connected with the hook, and the face, close to the tipping device, of the hopper is provided with ahanging lug hooked by the hook. Slag soil is loaded into the hopper, the electric hoist on the trolley elevates the hopper to the designated height, the carts carry out conveying, the slag soil is conveyed to the designated position, the tipping device tips the hopper, the slag soil is poured out, the slag soil can be automatically conveyed and tipped, manpower and material resources are saved, and work efficiency is improved.