The invention relates to a tobacco leaf puffing treatment device for preparing tobaccos in a tobacco factory, in particular to an improved novel tobacco shred expansion device. By the expansion device, expansion treatment is carried out on tobacco shreds which are soaked by carbon dioxide liquid and form dry ice by high-temperature airflow. The improved novel tobacco shred expansion device is in a Z-shaped tubular structure with an inlet and an outlet which are horizontally arranged, the inlet is connected with a hot air conveying device, the outlet is connected with a tangential separator, the position of the inlet is also communicated with a feeding mechanism, and the whole range of the tubular structure adopts an oblong section, wherein the area of the oblong section of an upright tubesection is gradually increased from an inlet end to an outlet end, the length of the longitudinal long axis of the oblong section is gradually increased, the length of the transverse short axis is unchanged, and hot air conveyed by the hot air conveying device is parallel to the direction of the transverse short axis in the direction of the inlet. The expansion device enhances the heat exchange effect of tobacco shreds in the expansion device greatly, also prevents the collision between the tobacco shreds and enhances the shred straightening rate.