Because of its excellent mechanical properties, slender rods with spiral structure have been widely used in engineering. Under the action of tensile and bending loads, the special structure of the twisted rods leads to the complicated deformation law. In this paper, based on the strain energy of slender rods and the Castigliano's second theorem in mechanics of materials, the displacements of the twisted rod under the action of tensile and lateral loads are obtained. The analytical results are in agreement with the finite element results. The calculation of displacement of twisted rod can be used as an extension of the basic content of mechanics of materials, which can strengthen students’ understanding and mastery of relevant knowledge points.