The Volume calculation model of big channels is established based on percolation echanics theory. The permeability calculation model of big channels is on the basis of high-speed non-Darcy fluid flowing in big channels. Big channels inunconsolidated sandstone reservoirs exist in incomplete developed form and complete development form. And the percolation indexes vary in different stages of development. Research results show that permeability of big channels when percolation index is 0.5 differs from permeability of big channels calculated according to linear Darcy flow with a ifference of 15.8 times. Confirming the percolation index n accurately is the premise of calculating permeability in big channels and the average radius.