A steam dryness modulating system comprises a steam generator, a gas collecting tank and three branches connected between the steam generator and the gas collecting tank in parallel, wherein the steam generator in the branch I is directly connected with the gas collecting tank to be in a normally opened state, a humidifying device is arranged in the branch II, a dehumidification device is arranged in the branch III, and a gas outlet pipe of the gas collecting tank is connected with a gas using device and is provided with a dryness meter. The steam dryness modulating system is characterized in that the steam of the branches converge in the gas collecting tank, the branch II and the branch III are switched according to a steam dryness value actually measured by the dryness meter, the steam leading amount is adjusted through a valve, and dry and wet steam mixing of different proportions can be achieved. In addition, automatic detection and control of steam dryness can be achieved by adding a signal controller. The united online pipeline steam dryness meter is applied to the system, and online real-time detection of the steam quality of the key working section of a tobacco shred production line can be achieved. Good steam quality can not only guarantee the tobacco shred processing quality, but also improve the energy utilization rate, and the service life of the valve and the device can be effectively prolonged.