This paper introduces the working principle of the test signal source of the aircraft power supply system based on DDS, and presents the realization of the threephase sine test signal source with FPGA+MCU. In view of the limitation of DDS (direct digital synthesis) circuit output waveform is limited by the limited memory capacity of ROM, the two ROM is used to store the sine wave data of one period, which reduces the high truncation spurious. The experimental results showed that the signal generator can output frequency accuracy of less than 0.1%, the amplitude accuracy of less than 3%, the threephase sine wave phase accuracy is less than 1%.