The invention provides a processing method for improving the quality of medium-and-low-grade tobacco leaves. The method comprises the following steps of 1, stem separation and screening, wherein stemsof raw tobacco leaves are cut off on a stem placing line, that is, the stems with the length of 10-15 cm are cut off in the main vein direction from growth portions of the tobacco leaves to leaf apexes; 2, vacuum moisture regaining, moistening, heating and humidifying, wherein the leaves without the stems in the first step are put into frames and subjected to vacuum moisture regaining in sequencefor 8-12 min at the moisture regaining temperature of 60-80 DEG C; 3, heat preservation, storage and impurity removal, wherein the tobacco loading frames are stacked in a concentrated mode after moisture regaining and sealed with canvas or plastic cloth to be stored for 2-6 h; 4, leaf moistening process parameter adjustment, wherein the required temperature of a primary moistening link is 55-65 DEG C, and the moisture content is 16-18%; the required temperature of a secondary moistening link is 55-65 DEG C, and the moisture content is 18-20%; the water content of a cooling area of a leaf re-baking section is required to be 6-8%. The method can be used for obviously improving the harmony of sensory quality and the chemical component content of tobacco sheet finished products after threshing and re-drying.