Abstract: A method for preparing a rubber for an elastomer of a flexible joint, includes: weighing hydrogenated nitrile raw rubber, a silica reinforcing agent, aramid fiber pulp, carbon black, liquid nitrile rubber, zinc oxide, stearic acid, an antioxidant, and a peroxide crosslinking agent; plasticating the hydrogenated nitrile raw rubber in a first internal mixer at 125-135° C., collecting a resulting product and cooling, to yield a plasticized rubber; preheating the liquid nitrile rubber; adding the plasticized rubber to a second internal mixer, further adding the aramid fiber pulp, the zinc oxide, the stearic acid, and the antioxidant to the second internal mixer for first mixing; adding the carbon black to the second internal mixer for second mixing; adding the silica reinforcing agent and the preheated liquid nitrile rubber to the second internal mixer for third mixing; and collecting a discharged product when a temperature of the second internal mixer is 140° C.