This paper describes modeling of the efficiency of fibrous filters using numerical simulation and X-ray computerized tomography (XCT). Variations in the flow field within the filter due to particle accumulation and structural inhomogeneities are taken into account in the mathematical model. Both the theoretical results and the experimental XCT data (digital images) showed that in the depth filtration process analyzed there is graded particle accumulation, Larger particles form bridges and can improve the collection for smaller particles during the filtration time. It is also found that smaller particles tend to promote a more pronounced pressure drop.