Coal bed methane has different petrophysics from conventional gas, and it absorbs in molecularity on the surface of coal. It is regarded as a component part of minerals contained in coal. The seismic velocity change resulted frommethane adsorbance is calculated. The result shows that P-wave velocity declined to 10%～16% due to the change of gas content, so it is also feasible using seismic technology to detect coal bed methane. The reflection amplitude has amplification effect on velocity change of coal, which conduces to detecting coal bed methane by using amplitude attributes. Using prestack inversion P-wave and S-wave impedance to calculate the elastic parameters of pore fluid can improve the detection accuracy of coal bed methane.