This article mainly analyzes the characteristics of the four-step braided technology, and simulates the motion track of the yarn according to the braiding characteristics in computer. It uses computer graphic technology to show the 3d braided structure, and simulates the design and implementation of braided composites with three-dimensional four-step approach. On the basis of the relationship of braiding parameters, simulation parameters are set in the computer software, so as to generate the 3d braided model in variety of sizes and angles, which can be infinitely close to the real structure model of the braid.