If the hydraulic gradient which caused by the underground seepage of mountain slope is greater than the critical hydraulic gradient of this area, the piping phenomenon occurs and which leads to a huge amount of damage. In this study, we start form a experiment of a model for heterogeneous layered piping phenomenon. The selected material was the standard sand with groups which was passed through the sieve of number thirty, retained on the number forty and the other groups passed through the sieve of number fifty, retained on the number sixty. The results from experiments can tell the magnitude of critical hydraulic gradient of the slope, and the fracture point is observed around the middle layered of the model slope. We also found that the discharge of ground seepage will be enlarged instantly when the piping phenomenon occurs till the slope was totally destroyed. The formula derived from Zhen (2007) is used in this study. We modified it with the different porosity caused with the different consolidation. According to this we could find different critical hydraulic gradient with different porosity. In this study, the simulation of heterogeneous piping phenomenon used FEMWATER, a commercial soft ware of Finite Element Method simulation. We simulated according to the results of experiments, such as soil properties and boundary conditions, and use the results of simulations, i.e. the velocity of seepage and hydraulic conductivity, to calculate critical hydraulic gradient. From the comparison between analytical solution, experimental result and FEM simulation, we have found that the critical hydraulic gradient of experimental is less than that from numerical simulation. And compare with different slope between 45 degrees and 50 degrees shows that deeper the slope, the piping phenomenon is occurred more frequently.