Abstract: The identification of the systems, It has become a new branch of the Science. On the identification of the machine tool dynamic systems, The frequency response method or the mechanical impedance test is applied generally. This method is complete. Its application has been gotten enough success. Now a new identification theory and method for the machine tool dynamic systems is proposed and studied by us. And the experiment is completed successfully. It is our identification theory and method that is to obtain the frequency response data using the complete frequency response test technique at first. Through the analysis and calculation by micro-computer, the transfer matrix of the system is identified. Based on the modern Control theory, using the state graphical method, through the transfer matrix the state space mathematical model of the system is obtained at last. This identification theory and method is appropriate for real systems which are multi-variable systems. The state space mathematical model is inside description of the system. Since it comprises more information of the system than others. The high order differential equation represented the system is converted the first-order differential equations. And it is the form of the matrix equations. So it is convenient for the sys-tem analysis and research by micro-computer. The modern control theory may be app-lied to analyze and to synthesize the system at the time domain directly. Furthermore the optimal design and optimal control for systems can be relaized. The application of the classtical control theory and modern control theory is conjoined. The use of the subsistent frequency response test equepment and the micro--computer is conjoined also. So this is a new identification theory and method for machine tool dynamic systems. It has general and important values.