Abstract: A cross section design method of a helicopter rotor blade based on topology optimization is proposed. The stiffness characteristics of a 2-D cross section are given using the finite element method. Both of shear and warping deformations are considered, and the coupling of warping deformation and rigid displacement is eliminated. The averaged compliance of a rotor beam or the stiffness of a cross section is adopted as the objective function. An optimization problem is solved based on SIMP algebraic with the rotor weight constraint condition. The derivative of an objective function is obtained, and Sequence Linear Program (SLP) is used. The results show that the averaged compliance of a Ⅱshape cross section is minimum when a rotor beam with a small span. An H beam would be the best when its span increases. In addition, final optimization results would be influenced by the load boundary condition. This method is suited for the design of the cross section of helicopter rotor blades in their concept design phase.