Research conclusions: (1) The appearance of the giant landslide in fluidity area reflected the features of the suddenness and the high － level and high － speed movement of gaint mud － stone flow．(2) The broken weathered granite rock mass and the unfavorable structural plane were the basic condition for landslide． (3) The effects of the heavy rainfall，loading and water softening along the steep under structural plane were the direct cause for the landslide．(4) After the landslide was rapidly gliding，the landslide disintegrated quickly and turned into mud － stone flow with water．Then the mud － stone flow constantly scoured the ditch bed to cause increasement of the water content gradually and quickly moved for about 4 kilometers．(5) The Qingshuiwan section of Hainan east ring railway and the eastern speedhway were located in the outside edge of the accumulating area of the mud － stone flow．When the mud － stone flow arrived at this place，its intensity was much weakened with less destroy degree．