Abstract：On the basis of the detailed geologic investigation results which were gained on the location of the barrier dam，combining the early information before earthquake，the forming process and blocking river mechanism of the landslide can be summarized as follows：(1) there were shearing surface in forward edge of the landslide on dip slope which was caused by earthquake and drawing open in back edge；(2) the air wave was formed by the high speed sliding，and the riverbed was ploughed by its forward edge，and the thither slope was uplifted for inhibition；(3) the back edge of the landslide stood and glided；and (4) then it dammed and blocked river. Meanwhile，according to the geological structure and different water levels of the barrier dam，the barrier dam¢s stabilities in upstream and downstream are studied. It is shown that the scouring mode of the barrier dam is overflow breakdown mechanism which stepwise scours the surface layer of loose media on the groove position，and the possibility of dam-breaking is small.
