Abstract: A multi-ratio transmission system is provided, including multiple planet gear sub-systems, at least two coupling assemblies, a setting element, a setting element controller, an annular gear, a cylindrical casing, a sprocket, and a central axle. The planet gear sub-systems are disposed coaxially in series along a first axis. Each of the planet gear sub-system includes a sun gear and at least one planet gear. Each coupling assembly transmits the rotation between every two adjacent planet gear sub-systems. The setting element optionally engages with the sun gear. The annular gear is installed onto a one-way clutch. The cylindrical casing encloses the planet gear sub-systems. The sprocket is installed onto the planet gear sub-systems through the one-way clutch. The central axle enables the hollowed tube of the setting element controller to rotate around the central axle.