NOVELTY - Producing bio-natural gas by biological desulfurization and carbon dioxide recycling coupling method, comprises dedusting crude marsh gas, using alkaline absorption solution for absorbing hydrogen sulfide and converting into sulfide, oxidizing sulfide to elemental sulfur, separating sulfur substance and mother liquor, adjusting pH of mother liquor for absorbing hydrogen sulfide, obtaining hydrogen sulfide of marsh gas, deeply dehydrating hydrogen sulfide of marsh gas, separating methane and carbon dioxide from obtained gas mixture to obtain high purity carbon dioxide and natural gas methane.    USE - The method is useful for producing bio-natural gas by biological desulfurization and carbon dioxide recycling coupling method.    ADVANTAGE - The method produces natural gas, biological sulfur and high purity carbon dioxide, which improves the economic benefits of marsh gas.    DETAILED DESCRIPTION - Producing bio-natural gas by biological desulfurization and carbon dioxide recycling coupling method, comprises (a) dedusting the crude marsh gas, using alkaline absorption solution for absorbing hydrogen sulfide and converting into sulfide, oxidizing sulfide using sulfur-oxidizing bacteria to elemental sulfur, separating sulfur substance and mother liquor, adjusting the pH value of mother liquor to alkalescence for absorbing hydrogen sulfide, and simultaneously obtaining hydrogen sulfide of marsh gas; and (b) deeply dehydrating hydrogen sulfide of marsh gas, obtaining the gas mixture, adopting cellulose acetate fiber or polyimide-based organic polymer membrane, separating methane and carbon dioxide to obtain the high purity carbon dioxide and natural gas methane. An INDEPENDENT CLAIM is also included for a device for producing bio-natural gas by biological desulfurization and carbon dioxide recycling coupling method, comprising a carbon dioxide removing system, where the carbon-dioxide removing system comprises a gas separation membrane module (12), and the gas separation membrane module is connected with a bio-desulfurization system through a gas pipe, which are orderly provided with a first pressurizing pump device (7), a first heat exchanger (8), a molecular sieve dehydration tower (9), a second pressure pump (10) and a second heat exchanger on the pipe of the gas flowing direction.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of the device for producing bio-natural gas by biological desulfurization and carbon dioxide recycling coupling method (Drawing includes non-English language text).    First pressurizing pump device (7)    First heat exchanger (8)    Molecular sieve dehydration tower (9)    Second pressure pump (10)    Gas separation membrane module (12)