The cracking gas compressor in the 1.1 Mt/a ethylene plant of PetroChina Dushanzi Petrochemical Company is a large unit with three cylinders and five stages. This article studies the problems in the long-term operation of this compressor including liquid entrainment in suction line, increased interstage pressure difference, interstage corrosion and increased displacement of high-pressure cylinder. By analyzing the insufficient capacity of the demister for interstage suction tank, the accumulation of coke particles inside the tube bundle of interstage heat exchanger, the high sulfur content of cracking raw materials and the severe coking in the fifth stage, some countermeasures are taken. By taking technological transformation measures, optimizing daily operation and adjusting the injection amount of polymerization inhibitors, the operating efficiency of the compressor is improved, thus ensuring the stable, long-term and efficient operation of the compressor.