Abstract: After releasing GB 39728-2020 Emission Standard of Air Pollutants for Onshore Oil and Gas Exploitation and Production Industry, the short-term SO₂ excessive emission during the shutdown period of sulfur recovery unit has become a potential environmental protection hazard in the oil and natural gas processing industry. The causes of SO₂ excessive emission in this special case were analyzed, and the emission of several sulfur recovery units during the period of sulfur removal were counted and studied. Moreover, this paper introduces the application of prewashing unit of tail gas treatment unit as alkali washing system in PetroChina Anyue Natural Gas Purification Co., Ltd during equipment maintenance and shutdown, which provides a new idea for SO₂ emission control during startup and shutdown or abnormal operation of sulfur recovery unit.