The rapid increase of new energy grid-connected capacity in China has brought great challenges to the security and stability of power grid. Firstly, from the two stages of low voltage and high voltage, the mechanism and process of voltage induced cascading off-grid accidents in new energy stations including wind power and photovoltaic stations are analyzed in detail. Then, a complete definition and model of the cascading off-grid path of new energy station are established, and the path search method and accident risk assessment system are proposed. Finally, a hierarchical control strategy of "hierarchical division" and "coordination" is proposed, which aims to block the cascading off-grid path to achieve the purpose of restraining the occurrence of off-grid accidents and is verified by the actual grid data.