This paper presents an on-line handwriting authentication system for text-independent Chinese handwriting. The proposed strategy is implemented on the stroke level, and the writing strokes and interstrokes are separated stepwise. The writing features are extracted from the dynamics of substrokes and interstrokes, including the writing velocity, the pressure, and the angle between the pen and the writing surface. To alleviate the effect of writing character number on the performance of the algorithm, we adopt the feature vectors of selected dimensions. In live experiments the authentication result is promising.