Abstract: The improved warp skeleton method was used to describe 3D woven composites architecture, and unit cell was decomposed into subcells/grids. The concept of crimp pattern code was put forward, and the yarn centerline could be fitted based on the information contained in the codes. With "mutual imitation method"of tows, cross-section contour line was fitted by sectioned spline curves. Merging centerlines and contour lines could derive yarns'curved surfaces, which were used to create geometric model of a preform. The obtained cross-section shape makes quite good agreement with SEM photoes. The results show that the sectioned spline curves can be used to describe the yarn pattern, and the efficiency of mutual imitation method is significantly higher than that of iteration one under the same precision.