In order to improve the airgap magnetic field distribution of hybrid excitation synchronous generator, a method named threelevel airgap length was introduced to optimize the rotor structure. The airgap flux densities, before and after optimization based on this method were analyzed and compared. After the rotor structure was optimized, the armature winding scheme with short pitch, distributed arrangement and skewed slots was adopted for a better voltage waveform quality. Then, prototype was tested to analyze its harmonic components of phase voltage with a power analyzer. Experimental results demonstrated that the total harmonic distortion (THD) of voltage could be restrained to the acceptable range(less than 5%) based on the combination of the threelevel airgap length and the stator skewed slots. Finally, feasibility of the eccentricdistance method used in the tangential/radial hybrid excitation synchronous generator was discussed, and the calculation results of airgap flux density were compared for the eccentricdistance method and the threelevel airgap length method.