There are phyteral cell remaining pore ,matrix pore and new -forming pore in coal.The pores of remaining phyteral cell mainly are complicated dentritic structure,and the effective porosity is high.Matrix pore and new -forming pore mainly are simple dentritis structure,the pore tortuosity is high,and the effective porosity is low.There are microfractures in coal matrix block,which are 10-20μm wide,50-1000μm high.Many of microfractures link with the pore,cleat and bedding fracture.methane diffusion distance c...