Abstract: Luoanjiang Irrigation-Reservoir Engineering Project was built during the first years after the foundation of P. R. C.,it is the one of the main water channels for irrigating more ten thousand mu land in the northern Guizhou,The 7.5 Flood Hazardoccurred in 1991 due to the extreme storm, river in spate,and underground stream back flow, resulting in high kinetie pressure. The bank slope and rockmass in which the unfavorable structural faces occur have undergone to on-beding landslide, blocked the mian channel and affected the inigation system seriously. The article analyses and evaluates the effects.of the landslide,its geological environment,structural features,the formation mechanism(landslide pattern and failure mechanism)and rockmass stability,as well as the genesis of landslide.