The utility model provides a steam quality modulating device, includes steam generator, gas collection tank and connects at these three branch roads that are parallel between the two that steam generator and gas collection tank directly link to each other for open state in I, is provided with humidifying device in the branch road II, is provided with dehydrating unit in the branch road III, gas collection tank's outlet duct and steam equipment meet and are equipped with the drimeter. The utility model discloses characteristics are that the steam of each branch road joins in gas collection tank, according to the steam quality value of drimeter actual measurement, switches branch road II and branch road III to the vapour volume is led to through valve regulation, the doing of different proportions, wet steam mix can be realized. In addition, signal controller's interpolation can realize steam quality's automated inspection and regulation and control. In using this system with the online pipeline steam quality of union type meter, can realize the online real -time detection of the crucial workshop section of tobacco cutting production line quality of steam. Good steam purity not only can ensure pipe tobacco processingquality, improves energy utilization, can effectively prolong the life of valve member and equipment.