A multi-gear mechanism includes first and second gear sets, an output set, multiple first planet gears pivotably connected between the first and second gear sets, a first gear ring having internal teeth and external teeth, multiple second planet gears cooperated with the internal teeth of the first gear ring, a second gear ring having internal teeth and side teeth, an operation gear ring and a motor gear. The motor gear extends through two central holes of the first and second gear sets, and the first and second planet gears are engaged with the motor gear. The operation gear ring is connected with the second gear ring which drives the operation gear ring to move axially. The motor gear drives the output set at low speed, constant speed or high speed when the operation gear ring and the second gear ring are operated to engage with different gears.