Rotary drilling rig and main winding floating system thereof

The invention provides a rotary drilling rig and a main winding floating system thereof. The main winding floating system comprises a main winding motor, a first reversing valve and a flow rate control device, wherein the first reversing valve is used for controlling the switching on and off of two oil ports of the main winding motor; the flow rate control device and a both way balance valve are used for controlling the flow rate of the two oil ports, and the two ends of the both way balance valve is respectively connected with the first oil port and the second oil port of the main winding motor; two ends of the flow rate control device are respectively connected with the first reversing valve and the first of the two oil ports; or two ends of the flow rate control device are respectively connected with the first reversing valve and the second of the two oil ports. According to the rotary drilling rig and the main winding floating system disclosed by the invention, the flow rate of a floating loop can be controlled, thereby regulating the speed of stably descending a drill pipe and improving the safety of the floating system of the rotary drilling rig.