In order to represent the difference between the handwriting motions, the impulse response of the FIR system is used. Because it can be seen that the FIR system and be completely characterized by its impulse response. In this case, the obtained impulse response is used as the feature of handwriting. Therefore, the writer recognition problem can be reduced to system identification problem. Finally, the K-L expansion of the impulse response of the FIR system is used for writer recognition.