The invention discloses a carbon-free-trolley shifting-fork synchronizer gear-shifting speed-changing mechanism comprising a front shaft, a rear shaft, a control circuit, a rear-wheel steering engine, an upslope front gear, a level-road small gear, an upslope rear gear, a level-road big gear, a first connecting rod, a second connecting rod, a third connecting rod, a push rod and a shifting fork. The shifting fork is arranged on the peripheral surface of the front shaft in a sleeving mode and moves in the axial direction of the front shaft, and shifting fork teeth capable of being inserted into axial holes of the inner portions of the upslope front gear and the level-road big gear are arranged on the side surfaces, facing the upslope front gear and the level-road big gear, of the shifting fork correspondingly. According to the carbon-free-trolley shifting-fork synchronizer gear-shifting speed-changing mechanism, a carbon free trolley walks at the road section of a level road through engagement between the upslope front gear and the upslope rear gear, or walks at the road section of an upslope through engagement between the level-road big gear and the level-road small gear, or walks at the road section of a down-slope through engagement between the upslope front gear and the upslope rear gear as well as the engagement between the level-road big gear and the level-road small gear so that the carbon free trolley of the embodiment can adapt to different road sections to drive, and the carbon free trolley has a wider application range.