The invention discloses a pulverized coal-biogas residue co-gasification system under a CO2/H2O steam atmosphere, comprising a biogas digester constant temperature fermentation system, wherein a fermentation liquid waste outlet is connected into a biogas slurry-biogas residue separating machine by the biogas digester constant temperature fermentation system, a biogas residue outlet of the biogas slurry-biogas residue separating machine is connected into a gasification system, biogas residues and pulverized coal are mixed and then are sent into a fluidized bed gasifying furnace in the gasification system, a gas outlet of the fluidized bed gasifying furnace is connected with a gasholder, a biogas outlet of the biogas digester constant temperature fermentation system passes through a desulfurizing tower and then is connected to a methane separator, and a gas outlet of the methane separator is connected with the gasholder and the fluidized bed gasifying furnace. A gasification raw material is a mixed raw material of the pulverized coal and anaerobic fermentation waste residues; the pulverized coal and the anaerobic fermentation waste residues are combined to produce a clean gas resource, and the problem that the fermentation waste residues are difficult to treat after medium and large scale anaerobic fermentation is solved; compared with single feed coal gasification, co-gasification of the pulverized coal and the anaerobic fermentation waste residues improves the gasification efficiency, and the fermentation waste residue resource is industrially utilized.