A high modulus graphite fiber with a tensile modulus of 270˜650 GPa and a plurality of crystal structures with a thickness (Lc) of 20˜70 angstroms is disclosed. Carbon fiber is used as a raw material, and a microwave focusing method is used to perform an ultra quick high temperature graphitization process to increase the temperature of the carbon fiber at a heating speed of 10˜100° C. per minute to a graphitization temperature of 1400˜3000° C., and then to perform a quick graphitization process for 0.5˜10 minutes to form the high modulus graphite fiber.