The fractal theory is a common method to predict the unsaturated permeability. But the theory can not be used in the computing of unsaturated permeability of Gaomiaozi bentonite in confined condition. The microstructure of bentonite changed a lot in the saturation process, and this phenomenon can not be reflected in the equations of fractal theory. The micro pores and macro pores of bentonite changed a lot in the saturation process which is different with the common sand or clay. With the consideration of Kozeny-Carman equation, a semiempirical-semitheorytical unsaturated permeability equation considering the microstructure of bentonite has been proposed based on the SEM test and MIP test of Gaomiaozi bentonite. The new equation was used in the analysis of unsaturated permeability of Gaomiaozi bentonite in the confined condition.