The open cavity flow contains various physical phenomena relating to vortex structures. The study on the vortex dynamics in the open cavity can provide theoretical insights into flow control and noise reduction. Direct numerical simulation is performed to obtain high order accuracy flow field of the open cavity. The vortex structures are identified using the Lagrangian coherent structures. Together with the Q-criterion and vorticity flux analysis, the formation, convection, impingement and split of the vortex in the cavity is studied and the dynamical characteristics are revealed. It’s found that the rolling up and shedding of Lagrangian coherent structures at the leading edge corresponds to the formation and shedding of the vortex. The split of Lagrangian coherent structures corresponds to the split of Q and Vortex. The main vortex in the cavity remains stable during the whole period of the flow.