The invention discloses a rotary drilling rig which comprises a chassis, a luffing mechanism and a power head, and further comprises a telescopic oil cylinder, wherein the telescopic oil cylinder comprises a piston cylinder and a piston rod; the piston rod can extend out or draw back relative to the piston cylinder; the drilling rig is connected to the lower part of the piston rod; the power head is connected with the piston rod and drives the piston rod to rotate; the power head transmits a torque to the piston rod of the telescopic oil cylinder, so that the piston rod drives the drilling rig to rotate; the telescopic oil cylinder also can provide downward pressure to the drilling rig to replace the action of pressing the oil cylinder in the original technology. The rotary drilling rig disclosed by the invention is relatively light in weight; a small number of steel materials are consumed; the production cost is reduced; the gravity center is relatively low; the stability of a rig body is improved; furthermore, parts are not required to denmount during transportation, and the transportation is facilitated.