Abstract: With the growing penetration of renewable energy sources, the problem of transient power frequency overvoltage caused by disturbance has become increasingly serious, which may lead to a large-scale off-grid accident of renewable energy sources and threat the operation of the grid. The low voltage ride through (LVRT) characteristics of the renewable energy sources directly affect the overvoltage level. There is an urgent need for in-depth research on overvoltage mechanism. This paper first analyzes the reason of overvoltage of high renewable penetration power system caused by AC symmetrical fault. Then a simplified model for analysis considering LVRT strategy of renewable energy sources is introduced. Further, after three-phase short-circuit fault clearance, the maximum overvoltage of the renewable energy source terminal is analyzed based on the vector relationship. Moreover, the influence of different LVRT strategy and system parameters on voltage rise is analyzed. Next, equivalent reactive current coefficient ranges avoiding off-grid accident are derived. Considering both reactive power support requirements of renewable energy during the fault and voltage safety constraints of renewable energy after fault clearance, the reasonable value ranges of the equivalent reactive current coefficient under different system strengths are analyzed. Finally, the time domain simulation is used to verify the validity of the theoretical analysis.