Abstract: Based on the analysis on variation characteristics of bottom hole pressure of coalbed gas wells during drainage and extraction phases, the whole drainage and extraction process of coalbed gas well is divided into pressure drop phase and stable pressure stage, the propagation laws of the pressure curve of coal reservoir in the two stages of drainage and mining under different reservoir boundary conditions are emphatically studied. The production curve is divided into four types:II, V, Λ and O according to the characteristics of pressure drop curves under open boundary condition, and four types:II, V₁,V₂ and V₃ under closed boundary condition. The pressure drop curve in the process of drainage and mining varies in shape due to factors such as boundary conditions, reservoir property and drainage and mining time.