Abstract: The framework of digital frequency modulation(FM) exciter is proposed, and the realization scheme of stereo signal composition and frequency modulation is studied. Combined with analysis and algorithm simulation, the design of hardware platform based on FPGA+DDS structure is accomplished. The performance of the signal after demodulation is analyzed by modulation analyzer and stereo decoder. Test results indicated that, compared with the conventional analog realization scheme, the signal synthesis method in digital FM exciter had simple structure and less error, and each parameter can satisfy the requirement of synchronization in broadcasting system, demanding exat unison in frequency, phase and modulation degree.