The invention discloses a tobacco stem preprocessing method used in a papermaking method sheet line. The tobacco stem preprocessing method includes the steps that tobacco stems are washed and dampened through a stem soaking machine after winnowing sundry removing is carried out on the tobacco stems, solid-liquid separation is carried out on the washed tobacco stems, and then the washed tobacco stems are conveyed into a feeding steam lock of a pressure stem moistening machine, wherein the frequency of a motor of the feeding steam lock ranges from 30 Hz to 50 Hz, the pressure of working steam in a drum of the pressure stem moistening machine ranges from 0.20 MPa to 0.50 MPa, the temperature ranges from 120 DEG C to 200 DEG C, the frequency of a spiral motor ranges from 30 Hz to 50 Hz, and the operating time of the tobacco stems in the drum ranges from 40 s to 60 s; the tobacco stems are conveyed to a discharging vibrating groove through a discharging steam lock, wherein the frequency of a motor of the discharging steam lock ranges from 30 Hz to 50 Hz, and the temperature of the discharged tobacco stems ranges from 70 DEG C to 90 DEG C; then the tobacco stems are conveyed into the papermaking method sheet production line to carry out the working procedures such as tobacco stem extraction, solid-liquid separation and pulping. After preprocessing is carried out, comparison detection analysis is carried out on tobacco stems after convention tobacco stem processing is carried out, and differences exist in hot water soluble matter, ethanol extract, the extracting efficiency, convention chemical components, the fiber structure and the dynamic water filtering performance.