Abstract: Based on the distinct element method of particle flow, a specimen with weak seam of Particle Flow Code (PFC) model is made by using the contact-bond model and the slip model. The numerical model test is carried on with different weak seam parameters. Then the paper discusses contrasting failure process and form under different weak seam thickness as well as different inclination angle conditions, and analyzes the influence to specimen strength. Simulation result indicates that fissures are produced first in weak seam and then are expanded with loading, which presents the typical progressive failure process. When the weak seam is thicker and its obliquity is steeper, the specimen presenting the feature to slide along with the weak seam becomes more obvious. But if it is thin and small, the weak seam doesn't dominate the destroying of the specimen. The thickness and obliquity of the weak seam have influence on the specimen peak strength. The peak strength is decreased when the thickness and obliquity are increased. The relation between the kind of failure characteristic and the geometric parameters is obtained from the numerical simulation. This relation offers a further understanding about mechanical property of weak seam and progressive failure.