Abstract: In order to deal with the difficulty of magnetic field adjustment in permanent magnet synchronous machines,this paper proposed a novel hybrid excitation synchronous machine （HESM） with parallel rotors,and described its basic configuration and the principle. Then,with the analysis of armature reactions,the detailed working performances of permanent magnet synchronous machine （PMSM） and the electro-magnet synchronous machine （EMSM） in HESM were introduced under different exciting current conditions. The operating modes of HESM can be classified into three categories:double-generation mode,single-generation mode and generation-motor mode whose boundaries were deduced. Finally,the experimental results proved the correctness of those analyses.