A method for producing the anode material of a lithium ion battery from flexible graphite powder, comprising (A) providing a dry flexible graphite, and pulverizing the dry flexible graphite by a pulverizing step, and filtering the dry flexible graphite with a sieve screen to obtain a uniform flexible graphite powder, (B) performing a ball-grinding step for the uniform flexible graphite powder by mixing with a solvent to obtain a liquid containing flexible graphite; (C) coating the liquid containing flexible graphite on a metal foil, and performing a rolling step to obtain an anode material. Then, the anode material is processed in its shape and is formed into an anode electrode plate. Thereafter, the anode electrode plate is stacked with a lower cover of the battery, a separating paper, a cathode electrode plate, a spring sheet and an upper cover of the battery to assemble the lithium ion battery.