This paper will be devoted to build a mathematical model of this kind based on the computer-controlled AC servo feed system of a common XY worktable. First, a practical AC servo worktable system is analyzed and its linear theoretical mathematical model is given. Second, the parameter in this model is identified in terms of the actual measured output data and reference signal by using an ARX model by using RLS identification method. Then, by using servo "simulation" techniques, a very accurate model of the servo drive can be constructed. Based on this model, it is possible to observe the effect on performance by changing the factors such as backlash, friction, servo-loop gains. Hence, a deep understanding of dynamics of the computer-controlled AC servo feed system of a common XY worktable is obtained. It is expected that this paper will lay reliable foundation for the further work-friction compensation, so that the precision of the system will be improved in the end.