In the process of lightweight design of structures, the topology optimization method does not depend on the experience of designers, so it can design the optimal products more flexibly and creatively, which has become a hot issue in structural design. However, the current topological optimization results usually have problems such as difficult processing and high cost, which limit their wide application in engineering design. Therefore, this paper is based on the two-way progressive structure optimization method (BESO), considering the existence of jagged edges in the optimization results. In the finite element analysis of the fixed grid method, the boundary element is judged by the sensitivity of the element node, and the boundary element is localized divide and realize the partial deletion of the unit, so as to achieve a smooth boundary of the optimization result. The sensitivity of element nodes during structural flexibility optimization is deduced in detail, its basic principles and specific steps are explained, and finally the feasibility of this method is verified by an example.