An improved permeation device was developed for the experimental investigation of the influence of different skeleton particle compositions with the consistent content of fine particle ranging (0.075 to 1 mm) on critical conditions of piping, erosion pattern and loss pattern of particles in the granular soil. The results show that for samples with different particle gradations, the hydraulic gradient and the seepage velocity exhibit a linear relationship before piping occurs, which essentially complies with Darcy’s Law. Skeleton particles in the size ranges of 1-2 mm, 2-3 mm, and 3-5 mm impede the development of piping, with particles in the 1-2mm range demonstrating a stronger blocking effect on piping voids than particles in other two size ranges. For skeleton particles of different gradations, the larger the heterogeneity coefficient, the larger the lower limit of the critical hydraulic gradient for the sample, making it more difficult for fine particles to be mobilized, and thus delaying the onset of piping. Conversely, the influence of the skeleton particle gradation on the upper limit of the critical hydraulic gradient of the sample is relatively minor.