Abstract: Coal matrix shape factor is an important parameter in studying numerical simulation and diffusion rate, so doing research on shape factor of different shape and size of matrix is meaningful. With assumption that the diffusion time is very long, the time-dependent factor is simplified to constant, so the expressions of factors of plate-like, columnar and spherical coal matrix, are obtained by solving diffusion equation in initial and boundary conditions. At the end, the conclusion is that the values of the three kinds of geometric shape present significant difference.