The invention relates to a tobacco stem sliver defining and detection method. The method comprises a stem sliver defining step, a tobacco shred moisture equilibrium step, a regression equation confirmation step and a stem sliver content detection step. Based on a large amount of data, the method can obtain a regression equation between primary winnowing rejecting substance content and actual stemsliver content through fitting; and it is proved that the method is obvious in regression effect and is high in applicability, and can quickly deduce actual stem sliver content in a cigarette.