With the large-scale grid connection of doubly-fed induction generator（DFIG） wind turbine generators， their impacts on the main system become more and more significant during system faults. The security and stability of the power system is under threat. To effectively evaluate the transient process and impact of DFIG wind turbine generators， it is important to understand the terminal voltage characteristics. In this paper， the expression of stator voltage under steady-state and three-phase short circuit condition is proposed based on the DFIG transient dynamics. Then the transient characteristics of stator voltage are investigated， and the effects of DFIG wind turbine generators on the main system voltage are studied. The changing patterns of stator voltage during system faults are further analyzed and verified by simulations.