NOVELTY - Recovering and processing liquid nitrogen washing device exhaust gas of large-scale ammonia synthesis, comprises removing carbon dioxide and hydrogen sulfide in the transformed exhaust gas via low temperature methanol washing, processing in a molecular sieve adsorber, conveying into liquid nitrogen washing cold box, processing in No. 1 raw material gas cooler and No. 2 raw material gas cooler, vacuum pressing in nitrogen washing tower, conveying into a hydrogen separator, flashing, recycling hydrogen, and performing depressurization and desorption to sodium formate producing raw material gas.    USE - The method is useful for recovering and processing liquid nitrogen washing device exhaust gas of large-scale ammonia synthesis (claimed).    ADVANTAGE - The method solves environment pollution problems associated with the exhaust gas of the washing device, improves utilization of waste resources, and ensures low cost production of high purity sodium formate.    DETAILED DESCRIPTION - Recovering and processing liquid nitrogen washing device exhaust gas of large-scale ammonia synthesis, comprises (i) increasing carbon monoxide content in a raw transformation exit from 0.2% to 1.8%; (ii) removing carbon dioxide and hydrogen sulfide in the transformed gas via low temperature methanol washing, conveying into a molecular sieve adsorber, processing, and then conveying into liquid nitrogen washing cold box; (iii) conveying raw material gas into No. 1 raw material gas cooler and No. 2 raw material gas cooler, cooling, then conveying into lower part of the nitrogen washing tower, removing carbon monoxide, arsenic and methane, washing liquid nitrogen at the tower top at -188 degrees C, and then conveying into bottom part of the nitrogen washing tower; and (iv) vacuum pressing the liquid at bottom part of the nitrogen washing tower, conveying into a hydrogen separator, flashing, recycling hydrogen in the gas-phase, re-heating in No. 1 raw material gas cooler, No. 2 raw material gas cooler and high pressure nitrogen cooler, introducing into liquid nitrogen washing cold box, low temperature methanol washing, pressurizing and recycling, discharging liquid from the bottom of the hydrogen separator, re-heating in No. 1 raw material gas cooler, No. 2 raw material gas cooler and high pressure nitrogen cooler, introducing into liquid nitrogen washing cold box, performing depressurization and desorption to obtain 50% carbon monoxide exhaust gas as sodium formate producing carbon monoxide raw material gas and then conveying into sodium formate production device, where the top part of the nitrogen washing tower is connected with outside of the liquid nitrogen pipeline.