Abstract: The gas-generating conditions of coal bed have influence on the accumulation of coalbed mainly by the gas yield in effective gas-generating stage.The gas yield in effective stage is dependent on the initial and terminal coal ranks of the effective stage,as well as the original abundance and composition of organic matter in coal.In this paper,a fundamental formula to estimate the gas yield in effective gas-generating stage is presented,and the recovery procedure to recover the original abundance and composition of organic matter in coal is discussed in detail.No.3 and 15 seams of the main mining district in the southen Qinshui Basin,Shanxi,are used as examples to estimate the gas yield in effective stage