The invention provides a humanized adaptive speed reducing system and a design method thereof. The humanized adaptive speed reducing system judges whether to forcibly reduce the speed of an arrival vehicle or not by detecting the speed of the vehicle and comparing the speed with a road section speed limit value, and consists of a speed reducing device, a transmission device, an electric motor, a transmission cable, a singlechip and a vehicle detection coil, wherein the speed reducing device is connected with the transmission device; the transmission device is connected with the electric motor; the electric motor is connected with the singlechip through the transmission cable; and the singlechip is connected with the vehicle detection coil. The design method of the humanized adaptive speedreducing system comprises the following steps of: setting a section speed limit sign, arranging the speed reducing device, pre-checking the speed of a running vehicle, comparing the speed with the section speed limit value, transmitting a command, judging whether to reduce the speed and recover a speed reducing initial state or not, and the like. Only the running speed of the vehicle is needed tobe measured and compared with a speed limit threshold value, so that whether the command is transmitted to the speed reducing device or not is judged, and the system is convenient to operate, has small construction investment, and can create good economic benefit.