The problem of synchronous data acquisition in the electronic transformer is analyzed. Meanwhile, the deficiencies of the synchronous data acquisition of the quadratic interpolation and cubic spline interpolation are pointed out. The accuracy of error is clearly insufficient in the quadratic interpolation with low sampling frequency. However, the boundary conditions of cubic spline interpolation significantly increase the amount of computation. The synchronous data acquisition based on the advanced third-order Aitken interpolation theory is put forward, and the error is theoretically analyzed and simulated. The result of simulation is matched with the theoretical analysis. Under the various atmospheres, the fundamental and the harmonic amplitude and phase angle’s error follows the standard of IEC60044-8. The advanced Aitken interpolation with higher precision and less simulation is easy to implement in the microcomputer measurement device, adapted to practical applications.