Hub driving system with built-in continuously variable transmission and clutch

The embodiment of the invention discloses a hub driving system with a built-in continuously variable transmission and a built-in clutch. The hub driving system comprises a belt wheel reducing device, a tensioning device, a hub and a steel wire cog belt, and the reducing device and the tensioning device are both arranged in the hub; the belt wheel reducing device comprises an input shaft, four fork arms, a cross-shaped sliding rail, a reducing electric cylinder and four belt wheel devices, the tail ends of the four fork arms are rotationally connected with one sides of the belt wheel devices respectively, the head ends of the four fork arms are hinged to the rear end of the input shaft, the reducing electric cylinder is arranged between the center of the cross-shaped sliding rail and the tail end of the input shaft, and the cross-shaped sliding rail and the reducing electric cylinder are hinged to the rear end of the input shaft. The other side of the belt wheel device is arranged on the cross-shaped sliding r