Synchronous generators with ac and do stator connections are widely used in systems where simultaneous ac and do power supplies are needed. For these systems the voltage harmonic distortion of ac voltage, do voltage ripple and do voltage varying range are of special interest. Because of the commutation of rectifier and the saturation of magnetic circuit, the accurate calculation of voltage harmonic distortion and do voltage varying range is comparatively difficult. This paper describes a mathematical model on the basis of multiloop method and FEM, which aims at calculating the steady-state characteristics and the voltage waveforms of ac winding accurately. With this method, the full synergic effects of space harmonics resulting from the magnetic circuit geometry, saliency, saturation, winding layouts, and slotting are included. The calculated results are compared with those of experiments.