Hydraulic shock absorber is widely used in vehicle. In order to study damping characteristic of hydraulic shock absorber, firstly the structure and working principle of a hydraulic shock absorber were analyzed. Then the four hydraulic shock absorbers purchased with machine were tested for damping characteristic on shock absorber test instrument, and the power indicator diagram was presented separately. The performance defects of the four hydraulic shock absorbers were analyzed by the power indicator diagram. The idle stroke distortion of the shock absorber was checked mathematically, which was consistent with the experimental results. The influence of the frequency on idle stroke was also analyzed. Finally the effect of the frequency on damping characteristic is tested, and the damping decay of the shock absorber is analyzed, which provide a reference for the improvement in design and use of shock absorber.