The invention provides a rotary drilling rig power head control device. The rotary drilling rig power head control device comprises a hydraulic pump, a main valve and a motor assembly, and further comprises a proportional valve and an entering-rock valve. The main valve comprises first valves, and the first valves comprises first main valve control ports. The motor assembly comprises power head motors. The main valve is connected between the hydraulic pump and the power head motors to connect or disconnect the hydraulic pump and the motor assembly. The proportional valve is connected to the first main valve control ports of the first valves to control the output flow of the first valves by adjusting the proportional valve, and the entering-rock valve is connected to motor control ports ofthe power head motors to connect or disconnect a pump-out oil ports and the motor control ports. By using the rotary drilling rig power head control device, the rotational speed of a power head of a rotary drilling rig can be controlled at any time by arranging the proportional valve and the entering-rock valve; and the device can be used for controlling the power head to be at the minimum rotational speed when drilling into hard rock strata while maintaining the largest torque of the power head, and the rock entering capacity is maximized.