Fibrous filters are widely used to remove particles from gas-solid flows. In the present research, the potential to enhance the collection efficiency of fibrous filters was investigated by increasing the number of filter rows and using varying sizes of square fibers. A two dimensional model was used to simulate the transport and deposition of particles, employing the developed Eulerian-Lagrangian solver coupled with the Immersed Boundary (IB) method. Several structures of filter fibers including the equal and unequal fibers in the arrangement of two, four and six rows were investigated. The results showed increasing the size difference between large and small fibers in the filter media increases the collection efficiency and pressure drop simultaneously. To find the effective structure of enhancing the filter performance, the quality factor was considered. The results of quality factor showed that using unequal fibers has an advantage over increasing the number of rows in an equal-fiber structure to increase the collection efficiency. Therefore, using the unequal fibers with the growth rate of 1.2 to 1.4, are more effective than increasing the number of rows in equal fiber structures.