In order to solve the problems of the current two different excitation regulator low excitation limit setting principles, this paper puts forward the low excitation limit setting principle that the action values of low excitation limit aer as close as possible to the measured leading phase capacity according to the different action characteristics of low excitation limit. This principle is based on the measured leading phase capability of the unit, and solves the problem that the low excitation limit setting principle of static stability limit is difficult to match the low excitation limit and loss of field protection because of the existing error of two devices, and can’t give full play to leading phase capacity. At last, this paper designs an optimized low excitation limit setting method based on current several different excitation regulators, which makes low excitation limit action value as close as possible to the measured leading phase capacity, gives full play to leading phase capacity and ensures the safe operation of the unit. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 521001160005) “Technical Measurement Research and Demonstration Application for Improving Support Capacity of Large-scale Urban Power Grid Voltage”.