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 and an annular gear. 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 is disposed between every two adjacent planet gear sub-systems so as to transmit the rotation. The setting element is disposed corresponding to each planet gear sub-system to optionally engage with the sun gear of the planet gear sub-system. The setting element controller is connected to the setting element of each planet gear sub-system to optionally move the setting element of the planet gear sub-system. The annular gear is engaged to the planet gear of at least one planet gear sub-system.