Abstract: The statics analysis and modal analysis of casting beam and welded beam of one double-column gantry machining center was carried out with ANSYS workbench. Advantages and disadvantages of the two structures were compared and researched. The results showed that through reasonably setting internal reinforcement plate of the welded beam,the weight of the beam was reduced by 10%,and the stiffness of the welded beam of gantry machining center was significantly improved. At the same time,the thin-wall flutter phenomenon of the closed frame structure with steel plate was effectively avoided. It provided a new thought for small batch,customer tailor of machine tools.