The study on the abnormal rotational speed phenomenon that occurs during the shutdown of a propylene compressor were conducted. By elaborating on the process principle and flow of the propylene compressor, systematically analyzing the changes in parameters such as the anti-surge valve position, rotational speed, flow rate, pressure, and liquid level during shutdown, and combining with on-site actual data, it clearly identifies that the main causes of the abnormal rotational speed are the small flow capacity of the anti-surge valve leading to backpressure and gas resistance at the outlet, as well as the excessively large retention volume in the compressor outlet pipeline. Corresponding improvement suggestions were proposed based on these findings to provide a reference for ensuring the stable operation of the propylene compressor.