Abstract: Geometry model of composites materials could be used to calculate its physical and mechanical properties. In this paper, a geometry modeling algorithm for composite materials with randomly distributed ellipsoidal grains and three dimensional braided composites is proposed. Firstly, we use ellipsoids to represent grains and modify the original samples of randomly distributed grains to remove overlapped ones. Then, in order to apply multi-scale finite element method, the ellipsoids outside the boundaries of the unit cell is handled to obtain the boundaries of matrix and reinforcement. For 4-step rectangular three-dimensional braided composites, we analyze the motion law of each yarn to obtain tightly packed yarns without intersection. Examples have been given to demonstrate the validity of algorithms.