Crazing is a kind of mechanism in toughening polystyrene by particles. In this paper, an independent elastomer particle unit is selected, and holes are embedded into the matrix (with cavities being represented by circular holes). Their diameter and distance are the same as cavities in crazing plane and the diameter of fibril. The crazing model is used to simulate the 1% strain crazing process with the finite element method. It is shown that the crazing initiates near the elastomer equator firstly, and is extended to the tangential direction. As the load increases, the fibril near the equator of elastomer is the first to reach the fracture critical value, then eventually crazing turns into crack. In this process, the fibril growth is in the direction of a certain angle with the load, which agrees with the experimental observation. From the elastomer with ?兹=30°, the molecular chains start to shrink because of the deformation of elastomer, then follows the materials contraction.