(1) establishing screening sets: establishing a decomposed gas type set comprising a plurality of unwanted decomposed gases produced from decomposition of an insulating gas inside the equipment operating under different operating conditions, and an original adsorbent type set comprising a plurality of adsorbents that potentially capable of adsorbing the unwanted decomposed gases;

(2) performing pre-experiment adsorption experiment screening: selecting each of the adsorbents in the original adsorbent type set to adsorb each of standard gases corresponding to each of the decomposed gases in the decomposed gas type set; then according to a change in mass of the adsorbent before and after the adsorption, a first suitable adsorbent for each of the standard gases is screened out and selected to establish a first adsorbent type set; the standard gases are one of single-component decomposed gases produced under a standard operating condition of the equipment, and plural-component decomposed gases produced under different operating conditions of the equipment;

(3) performing standard gas adsorption experiment screening: selecting each of the adsorbents in the first adsorbent type set to adsorb each of the standard gases corresponding to each of the decomposed gases in the decomposed gas type set; then according to a change in concentration of the decomposed gas before and after adsorption, a second suitable adsorbent for each of the standard gases is screened out and selected to establish a second adsorbent type set;

(4) performing mixed gas adsorption experiment screening: selecting each of the adsorbents in the second adsorbent type set to adsorb each of standard gases corresponding to the plural-component decomposed gases, or a mixed decomposed gas composition, produced under different operating conditions of the equipment in the decomposed gas type set; then according to changes in concentrations of a main insulating gas to be used in the equipment and the mixed decomposed gas composition before and after adsorption, a third suitable adsorbent for the mixed decomposed gas composition is screened out and selected to establish a third adsorbent type set; the main insulating gas is a gas component other than the mixed decomposed gas composition in a mixed atmosphere inside the equipment;

(5) mapping a relationship between the decomposed gas type set and the third adsorbent type set and based on the mapping relationship, selecting a combination of adsorbents suitable to adsorb the mixed decomposed gas composition; the mapping relationship is specifically a correspondence between an operating condition of the equipment, the mixed decomposed gas composition produced under said operating condition of the equipment and the combination of adsorbents suitable to adsorb the mixed decomposed gas composition produced under said operating condition of the equipment; and

(6) if there is no corresponding between the combination of adsorbents and the mixed decomposed gas composition under a certain operating condition of the equipment according to the mapping relationship, based on a molecular dynamics theory, constructing a structure of a simulated adsorbent combining the results of the three adsorption experiment screenings in steps (2), (3), and (4), and selecting a combination of adsorbents suitable for the structure of the simulated adsorbent.