Dynamical behaviors of granular piles are systemically investigated by an experimental equipment and imaging and direct particle tracking during quasi-static avalanches and slow flow process. It is found that part of beads slides obliquely downward, meanwhile the other part of beads is almost fixed; layer-structure can be clearly observed, and it include flow-layers and static-layer. The flow-layers lie almost parallel to each other and the angles between the flow-layers and horizonal plane are approximately in the range 4050. Moreover, the slippage of the flow-layers from the static-layer begins to gradually increase linearly. In addition, the positions of initial flow-layer that has different volumes of granular piles tend to be fixed.