As the length of the horizontal section in deep shale gas horizontal wells continues to increase, the cuttings produced during drilling are influenced by their own gravity and mode of motion, making them prone to deposition in the horizontal section annulus, which in turn affects the safety and efficiency of drilling operations. To address this issue, an efficient mechanical rock clearing device suitable for deep shale gas horizontal wells was designed. Retaining the advantages of conventional mechanical rock clearing devices, this device employed a two-stage design that changes the jetting method from continuous to intermittent pulsed jets, effectively preventing cuttings from invading the nozzles during transportation. Furthermore, numerical simulations were used to compare and analyze the fluid disturbances in the horizontal section annulus and the transportation of cuttings under different jet angles, blade structures, and mechanical rotation speeds. Based on the results of these numerical simulations, the device structure was further optimized. The results indicate that when the jet angle of the mechanical rock clearing device is within the range of 0° to 60°, the efficiency of cuttings removal in the horizontal section annulus gradually increases with the increase of the jet angle. However, when the jet angle exceeds 60°, the efficiency of cuttings removal in the annulus tends to decrease with the increase of the jet angle. When the blade structure of the mechanical rock clearing device features a spiral design, it achieves the best effect on cuttings removal in the horizontal section annulus; conversely, a V-shaped structure results in the poorest performance. If the mechanical rotation speed of the drill string does not exceed 70 r/min, the efficiency of cuttings removal in the horizontal section annulus will increase with the increase of the drill string's mechanical rotation speed. Conversely, when the mechanical rotation speed of the drill string exceeds 70 r/min, the efficiency of cuttings removal in the horizontal section annulus will decrease with the increase of the drill string's mechanical rotation speed.