This paper introduces the problems in the operation of low-pressure depropanizer of the separation unit in the 220 kt/a ethylene plant of PetroChina Dushanzi Petrochemical Company. Through the analysis of the material composition in the tower, it is found that the components that easily polymerize are mainly butadiene and cyclopentadiene and a small amount of styrene, and the scaling will cause the blockage of the bottom level gauge, resulting in abnormal display. The fluctuations in the operation of the low-pressure depropanizer are analyzed and discussed, the hazards are identified, and some corresponding preventive measures are developed, so as to ensure the long-term stable operation of the low-pressure depropanizer.