A multi-ratio transmission system with parallel vertical and coaxial planet gears is provided, including: multiple planet gear sub-systems, a coupling assembly, 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. The 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 engaged to the planet gear and is installed onto a one-way clutch. The cylindrical casing encloses the planet gear sub-systems. The sprocket is installed onto the one-way clutch for connecting an external transmission system. The central axle enables the hollowed tube of the setting element controller to rotate around the central axle.