Two-stage gearing bicycle

The utility model relates to a two-stage gearing bicycle, relating to the improvement of a gearing device of an existing bicycle. The utility model is characterized in that a big wheel disk is arranged on a middle shaft; an opening aligning to an annular groove of a rotating center is arranged on the inner side of the outer circumference of a big wheel disk; rolling wheels are uniformly fixed in the annular groove through small pin shafts. A stepped wheel is arranged on the bottom of a bicycle frame and is composed of a gearing gear and a gearing chain wheel, wherein, the gearing gear is engaged with the rolling wheels in the annular groove. The gearing chain wheel of the stepped wheel is connected with a flywheel of a back wheel through a chain. An automatic tightening wheel engaged with the gearing chain wheel is fixed at the bottom of the bicycle frame through a supporting frame. The utility model has the advantages of small radius of rotation, difficult chain falling and high bicycle speed.