For the problems of the generator no-load characteristics of poor measurement stability and excitation current base value difficultly setting, which are caused by excitation current measurement error in the excitation system modeling, the paper proposes a method to measure the excitation current by using the DC-side shunt method, and the sampling frequency is more than 30kHz and filter time constant is 0.2~0.3s through the analysis and comparison of the test site conditions, and excitation current measurement position and measurement mode. Finally, the method is applied to the excitation current base value setting of the 630MW unit, and the measured results are verified by the power system simulation software. The results show that the method can meet the engineering application requirements.