The utility model relates to a rotary dynamo. The stator of the dynamo comprises a stator rack which has a groove on the circumference of the stator and is arranged and installed along the hollow circumferential direction of a dynamo seat, an excitation winding which is winded along the groove of the stator rack and electric brushes which are respectively connected with two terminals of the excitation winding. A rotor comprises a parallel groove which is along the axial spacing of the preset distance of the hollow center of the stator, an armature rack which is provided with a commutator on both ends contacted with the electric bushes and an armature windings winded in the parallel groove of the armature rack. The stator of the dynamo can provides a very uniform rotating magnetic field for the rotor and does not generates the phenomenon of wasting the backset and the magnetism leaking. So the mechanical efficiency of the dynamo is relatively higher and can make the dynamo save electricity.