The invention provides a novel excitation loop design method for a large-scale synchronous generator. The method can guarantee consistency of rise speeds of excitation currents when self-shunt excitation units of different manufacturers, which have different parameters, perform excitation so as to guarantee a success rate of excitation. The method is characterized in that a current-limiting resistor is designed on a direct current side of a conventional excitation loop to adjust an excitation-rotor loop time constant so as to guarantee excitation success of the synchronous generator. According to the novel design method, firstly, based on an excitation regulator, a synchronous voltage is accurately detected; according to a principle that a current provided by the excitation loop reaches 20% of current intensity of i(infinity) within 5 seconds, the excitation-rotor loop time constant T is determined; and a resistance value of the current-limiting resistor is determined via computing so as to calculate a secondary voltage and a capacity of an excitation transformer, thereby completing the design of main components of the execution loop.