The invention discloses a pneumatic control device of a hydraulic speed governor. The pneumatic control device comprises a pneumatic speed governing part and a pneumatic parking part. The pneumatic speed governing part comprises a shell, a guide cylinder, a top cover, a governing screw, a linear ball bearing, a first retainer plate, a first membrane, a first piston, a thrust bearing, a first spring, a second spring, a high-speed limiting threaded sleeve, a first spring seat, a second spring seat and a speed governing rod; and the pneumatic parking part comprises a shell, a guide rod, a second retainer plate, a second membrane, a second piston, a third spring, a fourth spring seat and a parking rod. The pneumatic control device of the hydraulic speed governor has the functions of pneumatic speed governing and pneumatic parking.