The bed pressure difference of the cracking gas dryer in a 1.25 Mt/a ethylene plant had gradually increased since the startup of the plant and reached 65 kPa after two and a half years of operation. Some problems emerged, such as the poor heat transfer effect of heat exchanger in regeneration system, the blockage of coalescer in fuel gas system and the blockage of inlet filter in PSA unit. After disassembly, it was found that the blockage was mainly molecular sieve powder with a diameter of about 3 μm. In order to ensure the long cycle operation of the plant, it was decided to carry out online replacement of the agents for the dryer prior to the occurrence of water penetration. This paper mainly introduces the causes of molecular sieve pulverization and the subsequent measures taken.