Abstract: The extra large debris flow in Zhouqu county on August 8,2010 caused serious disaster which causing widespread concern of domestic and international engineering geological community.The investigation after disaster found that the former prevention and control projects were completely destroyed and the protection ability was breakdown.We should rethink it in order to learn this painful lesson.Based on the field investigation,through the discrete element simulation and theoretical analysis,the paper obtains some conclusions,such as the block dams are not strong enough against the stamping force of debris flow,the flow of the drainage projects does not match the cross-section,the flood discharge capacity is serious insufficient,there are too much curved conduits and the curvature is too big.Consideration and awareness of these issues will provide reference for the treatment scheme after the disaster.