Abstract— Contamination that exceeds the specification is one of many causes that contributed to a poor quality product in HDD cleanroom manufacturing process. The purpose of this research was to utilize CFD simulation to study the airflow in a clean room to find out the cause(s) of high contamination and to propose a remedy. The results of the simulation show that some areas in the production line had vortex flow and collected a large number of particles which were similar to the results of actual measurement in that clean room. A particular area, which was a long rectangular area near the middle of the clean room, stretching from one side of the room to the other, showed high particle concentration compared to other areas. To solve this problem, we closed one of the ULPA filters which was an inlet of that area. Subsequent simulation showed that there was less vortex flow and a significant reduction of particle concentration. Our method proved to be able to improve contamination control in a manufacturing clean room.