A new methodology for main bearing cap design was presented based on topological optimization and shape optimization. In topological optimization, filter functions of elements with respect to the unit volume and stiffness matrices were selected based on RAMP interpolation scheme. In shape optimization, efficient derivatives have been obtained by using approximate-difference strategy. Structural volume was taken as objectives and structural responses such as displacements, stresses were taken as constraints. This kind of model ensured consistency in topological optimization and shape optimization model. Volume of main bearing cap has been minimized subject to rigidity and strength constraints. The feasibility and efficiency of the proposed methods were demonstrated by the experiment.