Structure parameters have important effects on dynamic modeling and vibration control of the feed servo system of machine tools. It is meaningful to identify them accurately. Abundant information is included in the critical stick-slip velocity of the worktable. The new method of structure parameters identification is put forward by using the BFGS variable scale method, which is based on the relationship of the critical stick-slip velocity and structural parameters. The function relation between the critical stick-slip velocity and structural parameters is derived and the error function related with the structural parameters is established. The correctness and feasibility of the method is verified by numerical simulation of the motor direct connected feed system. In the field testing, the cross feed system of a heavy duty CNC machine tool is employed. The data of the critical stick-slip velocity at different feed positions are obtained by the Renishaw laser interferometer measuring system. The structural parameters of the feed system are identified satisfactorily. All the work can provide a theoretical and experimental reference for the identification and optimum of the structure parameters of feed systems.