Against the backdrop of large-scale new en ergy clusters and base construction，faults in the grid-connection lines of new energy collection stations may cause significant power disturbances，posing risks of inducing the cascading off-grid occurrence of new energy sources and deteriorating system frequency stability.To this end，this paper builds a coordinated expansion planning model for new energy cluster integration and regional power grids，with off-grid risks considered.Firstly，the main problems in the regional grid expansion planning under the integration of new energy clusters are analyzed.Subsequently，a coordinated planning model of new energy cluster integration and the expansion of regional power grid structures is built.Then，in the optimization of new energy station clusters，by considering the constraints of the utilization rate of grid-connected lines at the collection stations，the regional grid planning model takes constraints related to large-scale new energy off-grid risks under faults of grid-connected lines at collection stations into account，including the system frequency rate of change，frequency deviation，and post-fault line flow constraints.Finally，a case analysis based on the improved IEEE RTS- 79 system is conducted to validate the effectiveness of the proposed model and planning scheme.