The utility model relates to a bicycle, particularly a driving mechanism of a bicycle. The utility model comprises a front keyboard, a rear chain wheel, etc., and two fulcrums of the driving mechanism are respectively the front keyboard and the rear chain wheel. Another fulcrum of the triangular accelerating driving mechanism is arranged on a chain wheel group which is arranged between the front keyboard and the rear chain wheel and pivoted at a supporting base structure on a bicycle body with the upper part, and the chain wheel group is provided with a big chain wheel and a small chain wheel which can rotate coaxially; the front keyboard drives the small chain wheel to rotate through a front chain, and the rear chain wheel is driven by a rear chain and the big chain wheel. On one hand, the utility model has the function of increasing rotation speed of a small wheel on the rear part of the bicycle, and on the other hand, the center distance between the front keyboard of a pedal and the small wheel on the rear part of the bicycle is shortened, so the size of the bicycle body is reduced, and the bicycle can be carried and stored conveniently and run at the speed of the common bicycle with big wheels with the same pedaling force; the chain wheel group is arranged above the big chain wheel and the small chain wheel, so the situation that the chain wheel group impacts against a convex object higher than ground surface is avoided.