Stiffness analysis plays an important role in the optimization of the machine tool. By analyzing the static stiffness, dynamic stiffness and natural frequency of the key components, we discussed how to improve static and dynamic performance of the whole machine. Through the finite element analysis method, weak parts of the vertical machining center are firstly identified based on static stiffness analysis. Due to the purposes of increasing the stroke in Y-direction, improving the whole machine stiffness and without increasing the whole machine weight, optimal designs are carried out mainly on the structures of the spindle box and the column. And the performance of the parts and the whole machine before and after optimization is compared by testing whether the stiffness is improved or not. We also conducted experiments, and the results are consistent with the results of finite element analysis.