Abstract: One of the main objectives of High Frequency Surface Wave Radar (HFSWR) is to adapt the spectrum of transmit waveform to avoid narrowband interferences of wireless communication systems. Sparse frequency waveform that contains several individual clear bands and stop bands is a desirable solution to this problem. Besides spectral requirements, good correlation properties of transmit waveform are also desired in specific applications, such as the range side lobe. Moreover, practical hardware constraints require real-time algorithm which has a fast convergence rate. In this paper, a new penalty function is proposed based on both requirements for the Power Spectrum Density (PSD) and the Integrated Sidelobe Level (ISL). Then, the phase-only conjugate gradient method with very fast convergence rate is proposed to solve this problem. The proposed approach is efficient in computation and flexible in designing waveform. Optimized waveform can effectively suppress narrowband interference and have low ISL. The validity of the proposed method is illustrated by numerical example.