In the daily operation of modular cleanrooms, unstable differential pressure is a common and challenging problem. Stable differential pressure is a key indicator for maintaining cleanliness and preventing cross-contamination. Fluctuations can not only affect product quality but also lead to the failure of the entire purification system. This article will systematically analyze the four main causes of unstable differential pressure from a practical operation and maintenance perspective and provide a set of on-site troubleshooting methods.