Abstract: AC excitation technology of synchronous generator can improve capability of leading phase of generator,and it is one of the most effective methods of reactive power compensation.The paper proposed a design scheme of AC excitation power supply of synchronous generator based on hybrid modulation,analyzed composition and working principle of AC excitation system of synchronous generator,introduced control principle of hybrid modulation mode and gave selection and calculation method of key parameters of control circuit of the excitation power supply.The experiment result proved correctness and effectiveness of the scheme.