The purpose of this study is to investigate the influences of granular bed depth, gas velocity and granule diameter on the grade collection efficiency in a three-dimensional randomly packed granular filtration model. The simulation results and experimental results showed the effect of granular bed depth on the overall collection efficiency and pressure drop. It is found the pressure drop approximately linearly correlates with the granular bed depth. Then, the effects of granular bed depth, gas velocity and granule diameter on the grade collection efficiency were studied using simulation method, and the results indicated that increasing the gas velocity could improve the grade collection efficiency of particles greater than 7 mu m while it is useless for the particles smaller than 5 mu m. Increasing the granular bed depth makes the grade collection efficiency reaches the maximum earlier and it has equal promotion for the particles of all size. The grade collection efficiency is also approximately linearly correlates with the granule diameter and the granule diameter influences the position of the "turning point one" and "turning point two". (C) 2015 Elsevier Ltd. All rights reserved.