Abstract: By the experimental modal testing to the main structure of a high-speed horizontal machining center,the modal parameters such as the natural frequency,damping ratio,stiffness and mode shapes are obtained.By analyzing the dynamic characteristics,the weak links of this structure is at the spindle front bearing and the vertical column on which the screw driving the spindle box to move in vertical direction is mounted are determined,and provide an important basis of optimizing the structure for the machining center.And the amplitude-frequency characteristic curves of the weak structure evaluate the dynamic stiffness as the key indicators to provide reliable data for improving processing accuracy and cutting ability of machining center.The analysis results show that experimental modal analysis is a effective test method for improving the anti-vibration performance and machining stability of domestic machining centers.