The invention discloses and relates to a small-tooth-difference planetary reducer, a vehicle-mounted display screen device and a vehicle. The reducer comprises a reducer shell, an input shaft (220), an inner ring gear (230), cycloidal gears (240), an output flange (270) and a plurality of pin shafts (260); the inner ring gear is fixed on the reducer shell, eccentric cams (221) are arranged on theinput shaft, the cycloidal gears are installed on the eccentric cams through rotating arm bearings (285) and are meshed with the inner ring gear, and a plurality of pin holes (241) distributed in thecircumferential direction of the cycloidal gears are formed in the cycloidal gears; and the reducer further comprises a supporting frame (250), the supporting frame is provided with a central shaft hole (251), the input shaft penetrates through the central shaft hole, each pin shaft penetrates through the corresponding pin hole, and the two ends of each pin shaft are correspondingly connected withthe output flange and the supporting frame. The two ends of each pin shaft are supported, so that the bending strength and rigidity of the pin shafts are improved, and the pin shafts can keep consistent intervals all the time, so that the stress uniform load of all pin shafts is realized, and the overall bearing capacity of the reducer is improved.