Abstract: Coal reservoir has a large number of cleats and pores,which provide the essential condition for the storage of free gas.Free gas content in coal has big influence on CBM reservoir development.Through simulation test of the free gas content in coal with different particles,we measured the gas volume emitted after 12 h adsorption of methane in coal powder of different particle size,calculated the amount of adsorbed gas and free gas,analyzed the free gas content in fractures and pores of coal.The research showed that during crushing the destruction of fractures and pores in coal induced exposure of coal surface,reducing the storage space and the content of free gas in coal.For pulverized coal with different particle size,the free gas content ranges from 5% to 17% of the total gas amount,the bigger the particle size of coal powder,the larger the free gas content.