The invention provides a system for coupling aerobic composting and dry type anaerobic straw fermentation, and belongs to a biomass fermentation technology. The system comprises a biological carbon waste gas purifier, a dry type anaerobic straw fermenter and an aerobic composting device, wherein the aerobic composting device is communicated with the dry type anaerobic straw fermenter through a first waste gas conveying pipe equipped with a first gas valve; two ends of a biogas residue conveying pipe equipped with a biogas residue discharge valve are connected with a slag discharge port of the dry type anaerobic straw fermenter and a slag inlet of the aerobic composting device respectively; the biogas residue conveying assembly is assembled on the biogas residue conveying pipe; and the dry type anaerobic straw fermenter and the biological carbon waste gas purifier are communicated through a second waste gas conveying pipe equipped with a second gas valve. The system is simple in overall configuration, the technological process is novel and reasonable, the straw fermentation speed is high, the straw degradation rate is high, the production cost is low, and the environment pollution is low.