The invention discloses a circular oscillating tooth variable speed driving device with small teeth difference, consisting of an outer ring, a bearing pack, a driving ring, driving ring oscillating teeth, long oscillating teeth, short oscillating teeth, a ring gear, an eccentric shaft, a bearing, a rotary arm bearing, an eccentric bearing, a pin hole end cap, a pin tooth sleeve, a counter balance and a load balancing ring. In the driving device, the driving ring and the ring gear are meshed with small teeth difference, the meshed gear form is a cylindrical surface which can replace the traditional involute or cycloid, and the cylinder can rotate freely for convex-concave matching; a hole-pin type force transferring mechanism is adopted, a pin hole disk is arranged at the side and is integrated with the end cap, pins are selected from a plurality of cylindrical oscillating teeth and the pins and the teeth are integrated; the driving ring is an output mechanism. The whole shape of compact structure can carry out constant ratio variable transmission between input and output as a common rolling bearing can.