Abstract: In order to solve the issue of inability to evaluate the impact of power grid faults on renewable energy using the current power grid security and stability analysis, a method of calculating the voltage sag at point of interconnection (POI) and affected range of renewable energy under the faults in transmission network is proposed. Bounded by 220 kV nodes, fault voltage of 220 kV nodes is calculated by the improved fault calculation model considering the influence of current output characteristics of renewable energy. Based on the results, voltage at POI of renewable energy and the electrical distance between POI and fault point are calculated in typical scenarios for renewable energy integration into power grid. Finally, the proposed method is verified in the modified 39-node simulation system by comparison with traditional method and time domain simulation. The results show that, the deviation of fault voltage calculated by the proposed method is within −4.82%~0.6%, so the proposed method can accurately evaluate the influence of faults in transmission network on renewable energy. It can provide guidance for the optimization of renewable energy operation planning and control strategies.