In order to study the factors affecting the permeability coefficients of coarse grained soils, the sands used in actual engineers were applied , through the indoor permeability tests, different test conditions were used to study the effects of particle size, dry bulk density and relative compactness on permeability coefficients of coarse grained soils. The results showed that: for the same particle size composition of coarse grained soil, the permeability coefficient decreased with the increases of the dry density and the relative compactness. In the coarse sand range of average particle size, the permeability coefficient increased rapidly as the particle size increased, and when the average particle size was in the range of fine gravels, the permeability coefficient varied littleincreased as particle size increased. This research indicated that compression decreased permeability coefficients of coarse sand significantly, while affected permeability coefficients of fine gravels little.