The invention relates to the technical field of body-building equipment, and specifically relates to a soft rubber for a running belt. The soft rubber for a running belt is made of a raw material composition. The raw material composition includes the following substances by weight: 45 to 72 parts of polyurethane, 30 to 50 parts of nitrile rubber, 15 to 30 parts of styrene-butadiene rubber, 5 to 15parts of rare earth butadiene rubber, 5 to 25 parts of ethylene olefin random copolymer, 5 to 15 parts of metal oxide, 10 to 20 parts of diatomite, 3 to 5 parts of lysine, 3 to 8 parts of coupling agent, 0.5 to 2 parts of promoter, and 0 to 5 parts of auxiliary agent. The soft rubber for a running belt has high elasticity, high flexibility and high wear resistance, can buffer and absorb the impact force and vibration generated from running, and has long service life.