Disclosed are a method and a device for determining safe threshold for power grid voltage of a wind farm converging area, The method includes: obtaining ground state voltage; obtaining upper and lower limit voltage of the output bus, first lower and upper limit of reactive powers of fans and compensation devices, and lower and upper limit of active power fluctuations; obtaining second lower and upper limit of reactive powers of fans and compensation devices; determining whether voltage error is greater than a predetermined threshold; replacing the first lower and upper limit of the reactive powers of fans and the reactive powers of compensation devices with the second lower and upper limit of reactive powers of fans and compensation devices respectively, and repeating above steps if the voltage error is greater than the predetermined threshold, else defining the upper and lower limit voltage of the output bus as a safe threshold.