When the frame and the axle reciprocate relative to each other, and the piston in the shock absorber also reciprocates in the cylinder barrel, the oil in the shock absorber housing repeatedly flows from one inner cavity through some narrow pores into another inner cavity. At this time, the friction between the hole wall and the oil and the friction in the liquid molecules form a damping force on the vibration, so that the vibration energy of the body and frame is converted into heat energy, which is absorbed by the oil and the shock absorber housing, and then dispersed into the atmosphere. The magnitude of the damping force of the shock absorber increases or decreases with the relative speed of the frame and the axle (or wheels), and is related to the viscosity of the oil. It is required that the viscosity of the oil used in the shock absorber is as little affected by temperature changes as possible; And it has the properties of anti-vaporization, oxidation resistance and no corrosion effect on various metal and non-metal parts.