The invention provides a special drill bit for reverse circulation drilling, which relates to the technical field of reverse circulation drilling tools, and solves the technical problems of the existing reverse circulation drilling drills, such as the length of diameter protection, easy blockage and poor rock-carrying ability, the special drill bit for reverse circulation drilling It includes a drill base (10), a piston jacket (12), a pressurized piston (13), and a pressurized connector (18). The drill base (10) is connected to the pressurized connector (18) through a flat key (20), A piston outer rectangular ring (11) is sealed between the piston outer casing (12) and the drill base body (10), and a piston rectangular ring gas ring one (14), The piston rectangular ring oil ring (15) and the piston rectangular ring gas ring two (16) are connected. The invention can realize strong shearing and rock breaking ability in the drilling process, long-lasting diameter protection, easy rock carrying, strong suction, anti-blocking, self-pressurizing function, and has the characteristics of efficient and stable operation in the reverse circulation drilling process.