Abstract: A device and method for detecting an absolute multi-turn rotation angle. The device includes a housing, a cover plate and a rotating shaft. The rotating shaft is fixed with a main gear, which is meshed with driven gears including a large driven gear and a small driven gear. The main gear is externally meshed with the large driven gear. The driven gears are connected with a two-stage speed reduction device which enables the rotating shaft to rotate multiple circles to slow down to a circle-number gear and enables the circle-number gear to rotate one circle only. Both driven gears and the circle-number gear are provided with bearings. The bearings have magnets therein, and the two magnets are relatively fixed with the driven gears and the circle-number gear, respectively. The top edges of the bearings fit with a printed circuit board, angle sensing chips which are fixed on the printed circuit.