A belt drive system comprising a driving wheel, a driven wheel and a drive belt which is arranged on the peripheries of the driving wheel and the driven wheel to transmit motion, wherein the axis line of the driving wheel and the axis line of the driven wheel define a plane, and the drive belt comprises a first side portion located on one side of the plane and a second side portion located on the other side of the plane, wherein the belt drive system further comprises a first drive belt tensioning mechanism acting on the first side portion and a second drive belt tensioning mechanism acting on the second side portion, characterized in that the first drive belt tensioning mechanism comprises a first mounting seat, a first drive member threadedly connected to the first mounting seat, and a first tensioning device abutted against the first side portion, wherein the first drive member is abutted against the first tensioning device, and when the first drive member is operated to rotate relative to the first mounting seat, the first drive member moves relative to the first mounting seat and along the axis direction of the first drive member to drive the first tensioning device to move relative to the housing; the second drive belt tensioning mechanism comprises a second mounting seat, a second drive member in clearance fit with the second mounting seat, and a second tensioning device abutted against the second side portion, wherein the second drive member is threadedly connected to the second tensioning device, and when the second drive member is operated to rotate relative to the second mounting seat, the second drive member will rotate relative to the second tensioning device to drive the second tensioning device to move relative to the second mounting seat; and the first drive member and the second drive member are located on the same side of the plane. the belt drive system further comprises a first drive belt tensioning mechanism acting on the first side portion and a second drive belt tensioning mechanism acting on the second side portion, characterized in that the first drive belt tensioning mechanism comprises a first mounting seat, a first drive member threadedly connected to the first mounting seat, and a first tensioning device abutted against the first side portion, wherein the first drive member is abutted against the first tensioning device, and when the first drive member is operated to rotate relative to the first mounting seat, the first drive member moves relative to the first mounting seat and along the axis direction of the first drive member to drive the first tensioning device to move relative to the housing; the second drive belt tensioning mechanism comprises a second mounting seat, a second drive member in clearance fit with the second mounting seat, and a second tensioning device abutted against the second side portion, wherein the second drive member is threadedly connected to the second tensioning device, and when the second drive member is operated to rotate relative to the second mounting seat, the second drive member will rotate relative to the second tensioning device to drive the second tensioning device to move relative to the second mounting seat; and the first drive member and the second drive member are located on the same side of the plane.