In order that the CNC machine tool has to achieve very high process accuracy, the bed structure has to have a reasonable construction to meet this strict technical demand. The bed structure of machine tool as a important component is analyzed in order to be clarified about its vibration mechanisms. In this paper, the dynamic character of the bed structure of HTM40100 horizontal mill-turn compound machine center is researched by the finite elements method (FEM) in the circumstance of ANSYS, and modal analysis theory is introduced and applied. Bed structure is modeled as flexible body by FEM. The harmonic response and the modal results is given by calculation and running of the model in ANSYS. The bed structure of machine meets the technical demands well enough after those analyses.