A two-stage differential cycloidal speed reducer with a high reduction ratio is provided, including: a plurality of supporting crank shafts; an input shaft including a first crank shaft portion and a second crank shaft portion; a first cycloidal gear provided on the first crank shaft portion; a second cycloidal gear provided on the second crank shaft portion and connected with the first cycloidal gear through the supporting crank shafts; a plurality of first ring pins provided around the outer circumference of the first cycloidal gear and in sliding contact with a plurality of teeth on the periphery of the first cycloidal gear; a first annular gear with the plurality of first ring pins; a plurality of second ring pins provided around the outer circumference of the second cycloidal gear and being in sliding contact with a plurality of teeth on the periphery of the second cycloidal gear; and a second annular gear with the plurality of second ring pins.