Abstract: The rotary flow spillway tunnel with a blocker was proposed for meeting the requirements of the low pressure and cavitation erosion at high reservoir level. Then the characteristics of wall pressure, pressurization qualities and cavitations of flow with different blockers were analyzed by experimentation and theoretical methods. The results show that the wall pressures in whole tunnel are increased obviously because of the blocker, meanwhile, the negative pressures in the generator outlet are vanished. The increase reason of pressure in shaft is due to the pressure in its outlet, but in the spiral section it is associated with the radial distribution of tangential velocity and thickness of a flow layer. The increased pressures caused by a blocker vary along the tunnel, but keep constant in shaft and spiral section. Then the increased pressure expressions are put forward and verified by experiment. The cavitation erosion was also avoided by a blocker, by which, negative pressures and cavitations of flow with high velocity in the tunnel will be averted effectually.