With the improvement in management and technology in recent years, the operation cycle of ethylene plant is generally more than five years. It becomes more difficult for an ethylene plant to operate at full capacity at the end of its run cycle. Fouling is one of the main problems in cracking gas compressor and heat exchanger system. In the 5^th year of operation of an ethylene plant, high DP problem occurred in the heat exchanger at the outlet of the fourth stage of compressor. After fully evaluating the risks of heat exchanger damage and compressor surge, this problem was successfully solved by isolating a single group of heat exchangers for offline cleanup. A bottleneck of ethylene plant at the end of its run cycle was eliminated, enabling the plant to operate at full capacity in the 6^th year.