The invention relates to a tobacco stem soaking device for a tobacco stem washing machine, in particular to a device capable of conducting tobacco stem washing on puffing tobacco stems, and belongs to the technical field of tobacco machines. A water filter belt with a certain inclined angle and a transverse water filter baffle is added above a corrugated groove of the tobacco stem washing machine and in a water storage tank. According to the tobacco stem soaking device, a transmission shaft is driven by an externally-arranged motor to drive the water filter belt. When puffing tobacco stem materials fall into the water storage tank of the tobacco stem washing machine from a feed hopper, a filtration pore plate which is arranged on the circulatory-motion water filter belt can bring the puffing tobacco stems into the water and move towards the direction of an outlet, and meanwhile under the effects of circulating water flow and turbulent flow made by the corrugated groove, impurity cleaning is carried out on the puffing tobacco stems. When the filtration pore plate moves to the top end of the direction of the outlet, the filtration pore plate can be turned up, the puffing tobacco stems are released from the water along with turning up of the filtration pore plate, then, under the effect of the water flow, the puffing tobacco stems can be arrived at the water filter conveying belt, and the puffing tobacco stems enter back-end auxiliary-connected equipment.