Shock absorber capable of automatically holding tightly when being pressed

The invention discloses a shock absorber capable of automatically holding tightly when being pressed. The shock absorber comprises a main box, wherein a main shock absorption cavity is formed in the main box, a seal ring is fixedly connected to the upper wall of the main shock absorption cavity, a piston rod cavity opened upward is formed in the upper wall of the main shock absorption cavity in acommunicating manner, symmetrical holding block cavities are formed in the left side wall and the right side wall of the piston rod cavity in a communicating manner, a holding block is arranged on theupper wall and the lower wall of the holding block cavity in a left-right sliding manner, a holding mechanism is arranged in the holding block cavity, and the piston rod cavity is connected to a piston rod in an up-down sliding manner, and the piston rod extends downward into the main shock absorption cavity and upward to the upper side of the main box. By arranging the protective barrel capableof sleeving the shock absor