Abstract:Dynamic property of heavyduty machine tools directly connects with its machining accuracy,which is effected by joint surface and foundation.The stiffness and damping values of joint surface were obtained by fractal theory.In this way,the stiffness and damping values of each node with uneven load under the microstate of joint surface were introduced into a finite element model.Then,considering boundary conditions of joint surface,heavy duty machine tools-foundation system model was created.The modal analysis of the system was done by ANSYS FE software.Finally,the system model was validated by field measurement.The model was used to study effect to dynamic characteristics by changing the outline size of box foundation.The correctness of the mechanism design was evaluated,and the direction was pointed out for further improvement.