Abstract: Researches on stability of soil stratum permeability included studies of stratum structure,piping of sandy gravel,stratified piping of interbedded soil,irresistible force of nature,etc.In the past,only piping of sandy gravel was studied by various researchers.Analysis was made on piping stratum structure and stratified piping.By use of 453 groups of piping test data,verification was made to the existing 7 analytic methods for stability of soil stratum permeability at home and abroad.The filling coefficient theory was put forward,a criterion for the filling coefficient of soil stratum failure and a critical hydraulic gradient chart were formulated.The findings were applied in treatment of Yangtze River and Yellow River,and obvious achievements were obtained.The flood prevention and discharge capacities were increased,and the shipping capacity of Yangtze River was increased by more than 1.2 times.If these fruits could be kept continuously,disasters similar to Yangtze River Flood in 1998 would not happen again.