The invention discloses a rotary cutting device for road slope trimming. According to the device, a rotary cutting drum cutting head installed at the front end of a multi-stage telescoping hydraulic arm of the device is attached to the roadbed slope surface through a hydraulic operation rod and belt conveying operating button arranged on a hydraulic and belt conveying operating table, and the multi-stage telescoping hydraulic arm is lowered by lowering a multi-stage telescoping hydraulic arm lifting hydraulic cylinder to drive the rotary cutting drum cutting head to downwards conduct slope cutting operation on a roadbed slope and control the slope cutting speed; the rotary cutting drum cutting head rotatably cuts earth and stones on the roadbed slope surface, cut earth and stone aggregate is conveyed to a discharging port formed at the other end of a telescoping conveying belt through a wedge-shaped aggregate collected arranged at the back end of the device and directional rotation of the belt, and a forklift and a dump truck cooperate with each other to transport the redundant earth and stone aggregate on the roadbed slope surface to a specified storage site or a spoil ground to be stored. Accordingly, the phenomenon that the device is moved and carried by adopting other ways is avoided, and input of accessory supporting facilities is reduced.