The invention relates to a gas eliminating agent preparing method and a use method. A gas eliminating agent comprises, by weight, 37% to 44% of sulfonic acid, 26% to 32% of beer, 24% to 29% of gallic acid, 6% to 13% of cobalt carbonate and 3% to 7% of top yeast extract. The total weight ratio of all the mentioned components is 100%. The idea of passive prevention and treatment in the prior art is totally changed. The gas eliminating agent preparing method and the use method belong to the scope of initiative prevention and treatment. Basically speaking, gas is treated before coal is exploited and drilling is carried out on the ground when a mine is constructed. The gas eliminating liquid can effectively decompose mine gas when a coal layer is in a primitive state, the concentration of the mine gas is reduced, the gas is treated to be within a safety range, and personal safety of exploiting workers is ensured.