The invention relates to a device and a method for determining a coal grain adsorption and desorption law with accurate and adjustable parameters and belongs to the technical field of mineral engineering and safety engineering scientific research. The device mainly comprises a reference tank, a coal sample tank and a gas metering tank, wherein the reference tank is used for accommodating high-pressure gas; the coal sample tank is communicated with the reference tank through a pipeline; the coal sample tank is used for accommodating and adsorbing a coal sample of the high-pressure gas in the reference tank; the gas metering tank is communicated with the coal sample tank through a pipeline; the gas metering tank is used for accommodating the gas from the coal sample tank; solenoid valves are respectively arranged on the pipeline for communicating the reference tank with the coal sample tank and the pipeline for communicating the coal sample tank and the gas metering tank; respective corresponding pressure sensors are used for monitoring the pressure in the reference tank, the coal sample tank and the gas metering tank; the pressure signals are sent to a control cabinet by the pressure sensors; the signal is transmitted to a data processing unit by the control cabinet. A brand new structure is designed for the device, so that the determination for the gas adsorption desorption law on the coal seam under different existing conditions can be realized.