Abstract: In order to analyze the flow characteristics and collection efficiency of fiber in the internal pulp suspension field of forward cleaner,the internal pulp suspension field was numerically simulated with FLUENT software according to the swelling performance of fiber between dry and wet fiber, and combined with the concept of spherical fiber particle. The results showed that the particles track number of wet fiber a was higher than that of wet fiber b, while the two kinds of fibers from the accept outlet of forward cleaner, and according to the calculation that the collection efficiencies of fiber a and fiber b were 58% and 55%, respectively. The collection efficiency of fiber gradually decrease along with the increas of density, diameter, length of fiber, and the collection efficiency of fiber was not sensitive to the length of fiber. When the fiber length increased from 1 to 5 mm, the biggest drop value of collection efficiency of fiber was about 6%. The collection efficiency of fiber was sensitive to the density of fiber, and the biggest drop value of collection efficiencies on the two kinds of fibers was about 40% when fiber diameter changes from 10 μm to 70 μm.