The invention discloses a waste heat hardening and tempering process of motorcycle crank forged piece, comprising the working procedures like medium-frequency heating, extracting billet, blocking, precise forging, isothermal processing, quenching, tempering and the like. The process can obviously improve hardenability through forging waste heat hardening and tempering, ensure even distribution oftissues and hardness and ensure that the forged piece has the mechanical performance superior to that of the workpieces after conventional hardening and tempering. The workpieces undergoing finish forging adopt short isothermal processing to ensure the temperature of the workpieces to be uniform when entering quenching liquid, thus ensuring stable performance and excellent quality and realizing industrial production. Meanwhile, the short isothermal processing only consumes little electric energy, thus conforming to the requirement of the economical society.