The utility model provides a single-seat regulating valve for phthalic anhydride, and aims to solve the problem that most of the conventional regulating valves adopt thread screwing to control overflow of water, while as frequent screwing causes threads to be abraded easily or even flattened, the regulating valves cannot be used any more. The single-seat regulating valve comprises a valve seat (1); a sphere groove (2) is formed in the valve seat; three triangular clamping grooves (3) in the same straight line are formed in one side of the sphere groove vertically; a connection groove (4) is formed in one side of the valve seat, and is connected with a shaft sleeve (5); the shaft sleeve is connected with a rotating shaft (6); the rotating shaft is connected with a rotating plate (7); the rotating plate is connected with an upper housing (8); the upper housing is connected with a sealing ball (9); triangular spring plates (10) are connected to one side of the sealing ball, and inserted and positioned in the triangular clamping grooves; the sealing ball is pressed into and in tight fit with the sphere groove; the upper housing is connected with a handle (11). The single-seat regulating valve is used for regulating valves.