The invention discloses a technical method for purifying phosgene exhaust gas through a deep cooling process. The technical method comprises the following steps: firstly, causing the exhaust gas containing phosgene respectively pass through two or three serially connected condensers and condensing at different temperatures; feeding into an SN-7501 tower for catalytically decomposing and purifying phosgene; and finally, absorbing the exhaust gas with alkali and then directly discharging into atmosphere. When the exhaust gas passes through two serially connected condensers, the temperature of the first level condenser is -15 DEG C and the temperature of the second level condenser is -45 DEG C; when the exhaust gas passes through three serially connected condensers, the temperature of the first level condenser is -15 DEG C, the temperature of the second level condenser is -45 DEG C and the temperature of the third level condenser is -60 DEG C; and the first level condenser, the second level condenser and the third level condenser all adopt liquid ammonia for directly evaporating and condensing, so that the purifying efficiency is high, and the effect is good.