The invention provides a method and device for shearing an anchor cable in a supporting state. A shearing tool is formed by using a lock and a tray of the anchor cable, other high-strength shearing tools are not needed, hydraulic cylinders continuously provide shearing force, a lifting device lifts a shearing device without being operated nearby by personnel, injuries to personnel caused by an explosion phenomenon during anchor withdrawal are avoided, the whole device is flexible to move and easy to operate, and manpower and material resources are saved.