The invention discloses a coalbed methane group well extraction system and a construction method. The coalbed methane group well extraction system comprises a communicating expansion cavity, wherein the communicating expansion cavity is arranged in a coalbed; each ground horizontal well comprises a horizontal segment and a vertical deflection segment which are connected with each other; the tail end of each horizontal segment communicates with the communicating expansion cavity; the tail end of each vertical deflection segment extends to the ground; a plurality of horizontal segments are located in the coalbed; a first end of a suction pipe communicates with the communicating expansion cavity, a second end of the suction pipe is used for outputting coalbed methane, the second end of the suction pipe penetrates outside from the inside of a roadway and extends to the ground; and the part, in the roadway, of the suction pipe is a negative pressure pipe. The construction method is used for constructing the coalbed methane group well extraction system. According to the coalbed methane group well extraction system and the construction method, the mining range of the coalbed methane is improved, the energy consumption is reduced, the extraction cost of the coalbed methane is reduced, the ground construction cost is reduced and the laying cost and the operation and maintenance cost of drilling are reduced.