The invention provides a method for synthesizing an oxalate by carbon monoxide deep coupling catalytic reaction, and belongs to the technical field of oxalate synthesis. The method comprises the following steps: (1) mixing carbon monoxide and nitrite cyclic regeneration gas, preheating, introducing into a deep coupling catalytic reaction system to synthesize an oxalate, and separating to obtain gas phase circulation gas and liquid phase crude oxalate, wherein the deep coupling catalytic reaction system adopts a two-segment design, the first segment is a constant temperature shell and tube reactor, and the second segment is a fixed bed adiabatic reactor; (2) introducing the gas phase circulation gas in step (1) into a regeneration system, and reacting with methanol or ethanol to form a nitrite; and (3) performing multistage rectification of the liquid phase crude oxalate, and separating to obtain a refined oxalate product. The method provided by the invention adopts a two-stage deep coupling catalytic reaction system to combine the use of the constant temperature shell and tube reactor and the fixed bed adiabatic reactor, which not only can increase conversion rate, reduce equipment investment and reduce catalyst use, but also can reduce the regeneration system circulation and rectification separation energy consumption.