The invention discloses a protection device and method for demolition blasting flying stone of a supporting beam of deep foundation pit engineering. The device comprises a supporting framework. The supporting framework comprises supporting stand columns, connecting cross rods, three-way connecting parts, bearing components and adjusting components. The three-way connecting parts are arranged at the top ends of the supporting stand columns. The three-way connecting parts, the bearing components and the adjusting components are connected to form top supporting components. The connecting cross rods are fixedly connected with the supporting stand columns through the top supporting components. An upper supporting layer is formed by the connecting cross rods and the top supporting components. Protection nets are built on the upper supporting layer. According to the protection device and method, the design coverage area can be accurately achieved by selecting a method of combining steel frames and metal wire nets; and due to the fact that the strength of the metal wire nets is far higher than that of engineering cloth, the blasting flying stone can be blocked to the greatest extent. The steel frame structure of the device can be subjected to multi-piece splicing according to the shape of an actual blasting area, and the functions of conciseness and high efficiency are achieved. The device can be repeated, and the reliability of use of every time of the device can be guaranteed.