This invention relates to a method for preparing expanded tobacco stems, characterized in that the method contains steps as follows: purification, stem expansion, hypoxia heat retention (hypoxia heat retention refers to heating the expanded stems at hypoxia environment and maintaining the temperature), natural stacking, sorting, and packaging. An expanded tobacco stem product prepared according to this method has uniform size and color. Taste is modest and plain when it is combusted, which does not affect the original taste flavour. Expansion volume, the ratio of the expanded stems to the total stems, and quality are stable, which can be used as adsorption material. More important, expanded tobacco stems made from stems of different origin, texture and year according to this method have uniform odor component, which can not be acquired by other expansion technologies. This technology has met the requirement for product fabrication.