Coal bed methane well completion method

The invention discloses a coal bed methane well completion method and belongs to the field of petroleum drilling engineering. The method comprises the following steps: drilling is performed with a drilling fluid as a circulating medium until a first preset position is reached, wherein the first preset position is located above a coal reservoir; a casing is run into a shaft and is sealed with a stratum through cementing concrete; after a preset time interval for waiting on cement is up, the drilling fluid is replaced out of the shaft; drilling is performed with air as the circulating medium until a second preset position is reached, and the second preset position is located below the coal reservoir or located in the coal reservoir; a drilling tool is pulled out of the shaft. The air is taken as the circulating medium for uncovering of the coal reservoir, cementing and fracturing are not required to be performed on the coal reservoir, the problem that the permeability of the coal reservoir is reduced due to the