The invention discloses a method for synergetic extraction of coal bed gas in a caving type gob area and a lower coal bed. The method comprises the steps that firstly, a mine is explored, a horizontal well is constructed from the ground to a base plate of the gob area, carbon dioxide is compressed into the well for cleaning, and coal bed gas extraction is carried out; when the extraction amount of coal bed gas in unit time drops to 20%-40% of Qi, running and stopping circulate, the extraction pressure is reduced, and the re-extraction process is carried out again; when the extraction amount drops to be below 20% of Qi, carbon dioxide is injected for replacement, and extraction is carried out again; when the extraction amount drops to be below 20% of Q1 again, the horizontal well and a coal and rock strata of the lower coal bed are subjected to fracture, and coal bed gas discharge and extraction are carried out; when the extraction amount drops to be below 20% of Q2, supercritical carbon dioxide replacement is carried out; and when the extraction amount drops to 10% of Q2 through extraction, extraction is stopped. By means of the method, synergetic extraction of coal bed gas in the carving type gob area and coal bed gas near a low coal seam is achieved, cost is reduced, and the coal bed gas resource is extracted to the greatest extent.