Air filter leakage is one of the most important control point for verification and qualification of cleanliness of cleanrooms. In this paper, a model that expresses the number of penetrated particles through high-efficiency fibrous air filter with pin hole is proposed, by using 3 dimensionless parameters for the fundamental study of establishing filter leakage testing method. Leak rate and limitation of judgment caused by the difficulty of identifying the leakage particles from all the particles are calculated. The result of the calculation is that the face velocity have a great influence on the leak rate and limitation of judgment.
