Abstract: In the crowded spectrum environment, the interference of the same frequency narrow-band has great influence on the detection performance of radar system. For this problem, sparse frequency waveform is a good solution. The waveform has the characteristic of sparse distribution on the spectrum, which can effectively suppress the same frequency interference. The low sidelobe property of the auto-correlation function ensure the detection performance of radar. In this paper, a method of designing sparse frequency waveforms by using complementary code is proposed. Firstly, considering the auto-correlation function of two sequences, the objective function is established by using the good auto-correlation of complementary codes. Secondly, the sparse frequency waveform is designed respectively by using power and sidelobe constraints to adapt the different scene requirements. Finally, the performance of sidelobe suppression is analyzed by numerical simulation to verify the effectiveness of the optimization design method.