Noncircular fibers have larger specific surface area compared to the circular cross-section fiber with the same volume fraction and may perform higher collection efficiency of submicron particles. In this article, we use a lattice Boltzmann-cellular automata (LB-CA) probabilistic model to simulate the particle filtration processes of four kinds of noncircular fibers with rectangular, trilobal, quatrefoil and triangular cross-sections at low Reynolds number (less than 1). The pressure drop and collection efficiency for the diffusion dominant regime, where the Peclet number ranges from 235 to 1000, are investigated. By normalizing the pressure drop and collection efficiency of noncircular fibers with those of the circular fiber, which can be calculated from the existing classical expressions developed in the past, the corresponding ratios are gained. Then the Levenberg-Marquardt algorithm is used to obtain the fitting expressions of the above ratios. The proposed easy-to-use fitting expressions can be used to calculate the pressure drop and diffusional collection efficiency of noncircular fibers under different operation conditions, when the fiber volume fraction is 5%-10%. The results show that the pressure drop of noncircular fibers is dependent on the orientation angle and the aspect ratio. The diffusional collection efficiency is almost independent of the orientation angle but proportional to the aspect ratio for all the noncircular fibers. (C) 2016 Elsevier B.V. All rights reserved.