After 3 years’ operation of the cracking gas compressor in the 220 kt/a ethylene plant at PetroChina Dushanzi Petrochemical Company, the bearing shell temperature of the thrust bearings TE12820/21 in high pressure cylinder reached 120℃/121℃ (120℃ is the alarm value) and approached 125℃, which is the interlock value of compressor. The causes of this phenomenon were analyzed, and the severe coking of the impeller and flow channel of cracking gas compressor was identified as the main reason for the temperature rise of bearing shell. Some measures including adjusting the lube oil temperature, increasing the water injection rate, adjusting the injection rate of additives and installing lube oil filtration system were taken, and good effect were achieved. The bearing shell temperature of TE12820/21 dropped from 120℃/121℃ to 113℃/110℃, ensuring the smooth operation of cracking gas compressor, avoiding the unplanned shutdown of the ethylene plant and even the shutdown of the whole plant as a result of abnormal bearing shell temperature, and remarkably reducing losses.