The invention relates to an improved method for acquiring the per-unit value of the excitation current under a traditional xad base value system. The method includes the following steps: S1, establishing a synchronous generator sixth-order practical model in consideration of the influence of saturation; S2, analyzing a parameter identification error by using the reference current ifB of an excitation winding under the xad base value system; and S3, accurately identifying generator stable-state parameters Xd and Xq by using the actually measured no-load rated excitation current iff0 (known value), the synchronous phasor measurement device PMU measurement data, and the dq winding base value, and calculating accurate excitation winding base value through Xd, if0, and forming a complete measurement data per-unit value. The method improves the identification accuracy of the generator parameters on the premise of following the principle of the traditional per-unit value system.