A gray-scale driving method for a bi-stable chiral nematic liquid crystal display is provided. The present method divides an updated picture into a first-section frame, a second-section frame and a third-section frame. The present invented method includes to drive the first-section frame into a predetermined initial state, and drive the second-section frame by line-by-line scanning by writing updated gray-scale frame data into the pixels, then pull the third-section frame to zero voltage for the pixels such that bi-stable chiral nematic liquid crystal relaxes to stable states corresponding to the write-in gray-scale frame data. Meanwhile, a purpose to maintain the updated picture without any consumption of power is obtained. The total power consumption can be significantly reduced.