When the steel grade and gear blank size have been determined, whether the quenching and tempering depth meets the requirements can be judged by calculating the section hardness distribution with known gear material and round bar diameter. When the gear size parameters are determined, it is necessary to select the appropriate steel to meet the technical requirements of quenching and tempering, and the determination method of calculation section size can be used. This method mainly considers the approximate maximum section size of the gear blank.