The invention relates to the field of transportation, specifically an energy-free downhill auxiliary system for a subway station and a railway station; the system is located at one side of a staircaseand comprises a first wheel, a second wheel, a main transmission belt, a connecting block, a third wheel, an auxiliary transmission belt, a box placing table and a water tank, wherein the first wheelis located at the top of the staircase and the first wheel is provided with a connecting shaft. The first wheel is connected with the second wheel by the main transmission belt and the main transmission belt is provided with clamping strips, which can limit a luggage case and enable the main transmission belt to move due to the gravity of the luggage case. The transmission system provided by theinvention is driven by the gravity of the luggage case and is economical and energy-saving. The auxiliary transmission belt is arranged for transition to prevent luggage from piling up at the bottom of the stairs and affecting the movement of the main transmission belt. The water tank connected with the first wheel is arranged, and non-Newtonian fluid is arranged in the water tank; the greater theweight of luggage on the main transmission belt, the greater the resistance of non-Newtonian fluid when the luggage rotates, so as to ensure that the rotation speed of the main transmission belt is not too fast.