Yeniu gully is a representative debris flow gully in the middle reaches of Dadu River. The ample source of materials and terrain change create appropriate conditions for the formation of next debris flow. Based on the study of solid material discharge, and the gully-bed condition of fan by debris flow from Yeniu gully under three different frequencies, the conventional empirical blocking formula was revised. The revised formula was verified by the study on debris flow in the Jintang River in Yeniu gully. The results showed that Jintang River will be completely blocked when P=1%, and partially blocked when P=2% and never blocked when P=5%. The test indicated the generality of the revised formula, which can be applied in the middle reaches of Dadu River.