The invention relates to a bicycle gear shifting device and a back-and-forth pedaling tricycle. The back-and-forth pedaling tricycle comprises a tricycle frame, a reclining seat, pedal plates and the bicycle gear shifting device. The bicycle gear shifting device comprises a driving shaft and a driven shaft, which are parallel to each other and fixed on the tricycle frame through bearings; a first chain wheel, a second chain wheel and a plurality of driving gears are sheathed on the driving shaft; the first and second chain wheels are respectively arranged on the driving shaft through positive clutches; the driving gears are respectively arranged on the driving shaft through reversing clutches; a plurality of driven gears are arranged on the driven shaft; and the driven gears are correspondingly connected with the driving gears in sequence to form a gear group with a plurality of speed ratios. In the invention, the structure is simple, the operation is convenient, the one-step gear shifting is realized, the labor is saved and the efficiency is improved via the back-and-forth pedaling, and the stability and the comfortableness of the tricycle is improved via three wheels and the inclining seat.