The non-parametric estimator of spot volatility is the current focus due to its high accuracy.However, this estimator has to choose the optimal bandwidth in its application.There is difficulty in calculating the optimal bandwidth since some awkward unknown parameters emerge.In this paper, taking kernel estimator as the representative of non-parametric estimator for spot volatility, a data-driven algorithm of bandwidth selection has been constructed by adopting some idea of non-parametric regression.The stability of algorithm for selecting bandwidth is proved in the theory.It is shown that the ...