The 1100 kt/a ethylene plant of Dushanzi Petrochemical Company was equipped with two cracking gas dryers, one for operation and one standby. A single dryer was designed to run online for 36h and then switched for regeneration. The online operation cycle of a single cracking gas dryer was extended to 72h, in order to reduce the influence of regeneration times on the adsorption performance attenuation of molecular sieve and to respond to the call of ethylene plant to improve quality and efficiency. After 11 months of optimized operation, the pressure difference of the dryer increased by 8kPa, leading to the increase of outlet pressure of cracking gas compressor and affecting the long-term and optimum operation of the plant at full load. In this paper, the factors causing the abnormal pressure difference rise are analyzed and discussed from the aspects of material composition, regeneration medium, residual adsorption capacity, feed temperature and regeneration process. Through the combination of theoretical calculation with practical production, some measures for optimizing the operation of the dryer in stages were proposed and adopted, solving the problem of abnormal pressure difference rise and realizing both stable operation and cost saving.