Abstract: A differential equivalent medium theory method and Biot consistent theory method were applied to an inversion on the pore aspect ratio and crack density of No.3 primary structure seam and overlaying coal measure strata in Shanxi Group of Guxian well block in Qinshui Basin.The results showed that No.3 primary structure sea m was mainly close spherical pore space system. In the overlaying mudstone,there was a pore and crack type multi pore space system. With the crack density increased,th e crack and pore degree of the coal measure strata would steadily be a maximum in tendency and meanwhile ,the rock volume modulus would be reduced obviously and th e crack density inversion results would have a certain reference value to guide the exploration of the coal measure gas.