Abstract: The geological background,overlying strata and buried history of coal measures,coal rank distribution and coal metamorphic characteristics in Tiefa Basin are analyzed comprehensively.It is considered that the coal metamorphism in tiefa Basin is dominated by the hypabyssal telemagmatic metamorphism;the timing,condition and way of the generation of coalbed pyrolysis gas are controlled by the coal metamorphism process;coal metamorphism and coalbed gas are both aspects of the same thing under the same geological environment.