Abstract: A control structure for a pneumatic sealant gun, which comprises a handle and a sizing assembly; both of them are able to be assembled together in a detachable manner so as to adapt to different type of sizing assembly. Both front and rear hoods of the cylinder of the sizing assembly are mounted with two connectors respectively; each connector is then connected to a connector on the rear side of a valve switch in the handle. The cylinder includes a piston therein with a guide shaft extended to the front hood. The handle is furnished with an air-supply trigger assembly to control the intake and exhaust of the sizing assembly of the pneumatic sealant gun.