The invention relates to a system and a method for judging competitive field intensity of gas adsorption and desorption. The system comprises a methane tank, a valve, a pressure gauge, a pressure regulating valve, a reference cylinder, a vacuum pump, a clamp device, a high-voltage power source, a constant-temperature water bath box, a flow rate sensor, a gas collecting box, a computer and a gas water drain device, wherein the clamp device comprises a cylinder body, and a coal sample cylinder is arranged in the cylinder body; a left electrode plate and a right electrode plate are arranged at both ends of the coal sample cylinder, and are respectively connected with an anode and a cathode of the high-voltage power source; the methane tank is connected with a gas inlet of the clamp device; agas outlet of the clamp device is connected with a gas exhaust pipeline, and the tail end of the gas exhaust pipeline is connected with the gas collecting box; the gas water drain device comprises a first metering cylinder and a second metering cylinder; the first metering cylinder is connected with the gas outlet of the clamp device, and the first metering cylinder is connected with the second metering cylinder. The system and the method have the advantage that the gas adsorption and desorption are measured by externally adding different electric fields, so as to obtain the gas adsorption anddesorption rule, find the competitive field intensity of gas extraction rate, and provide powerful experiment support for the recovery of coal beds.