The invention relates to a device and a method for improving gas extraction concentration. The device comprises a gas extraction pipe, a metallic net cage, activated carbon blocks, a gas concentration sensor, an electromagnetic valve and the like, wherein the activated carbon blocks fill up the metallic net cage; the metallic net cage is contained in the gas extraction pipe and is lowered into an extraction borehole together with the extraction pipe; the gas concentration sensor is tied on the outer wall of the extraction pipe in the borehole; the external portion of the borehole is connected with the electromagnetic valve, and a control console on the electromagnetic valve can automatically control the opening and closing of the electromagnetic valve by reading gas concentration change on the gas concentration sensor. By using the huge adsorption difference of the activated carbon to methane molecules under a variable-pressure effect, gas which is stored in advance is desorbed intensively by the activated carbon when the valve is opened, the extraction concentration of borehole gas is effectively improved and the problems of slow gas desorption speed and low extraction concentration during traditional gas extraction are solved.