A combined fracturing and perforating method and device for oil and gas well are disclosed. The method utilizes an explosion of a perforating charge (5) in a combined fracturing perforator to ignite primary gunpowder in the perforator, and burning of the primary gunpowder ignites secondary gunpowder in the perforator. The body of the perforating gun in the combined fracturing and perforating device is provided with pressure releasing hole (8) which is directly facing the jet direction of said perforating charge, and sealing sheet (9) is arranged on said pressure releasing hole (8). Inner gunpowder box (6), which contains the primary gunpowder, and outer gunpowder box (7), which contains the secondary gunpowder, are mounted on the cylindrical charge frame (4).