With rigorous fuel consumption regulation and emission law implemented, accuracy requirement of design and measurement signal is increasing, it becomes more and more indispensable to consider the influence on pressure loss and flow behavior coming from the incrementally loaded dust on filter element of Air Intake System (AIS). Dust is composed of many different sizes of particles, and studies shows that these different sizes of particles have very distinct influence on pressure loss of filter elements, which makes dust a challenge to model in Computational Fluid Dynamics (CFD) simulation. In order to precisely simulate pressure loss behavior of dust loaded filter element, a methodology for 3-D CFD dust loading simulation is developed, where the influence of particles sizes on pressure loss of filter element are taken into consideration by introducing a pressure loss weighting factors. And a steady CFD method is used here to simulate the transient dust loading process on a filter element, with the help of mass weighting factors. A study case using presented method is presented as well, and the result shows great consistency with test result.