Abstract: We proposed and used pore fluid pressure test method to study crack development laws of coal seam group mining area, and verified this method by the ground drilling extraction coal bed methane test. The researching results show that roof strata in the range of 7 to 43 m above the mined coal-bed belongs to water flowing fractured zone in the direction of height; floor strata of 18 m below the mined coal-bed belongs to floor fractured zone; in the direction of advancing of working face, the cracks fully develops at the location of 120 m after working face, and the cracks are gradually compacted after 120 m; the coal bed methane product of surface borehole successively experiences four processes, that is product declining process, product rising process, product relatively stable process and product declining process. And the coal bed methane product reaches the summit at the location of 120 to 130 m after working face, and this is fully coincident with the results of cracks development laws experiment.