Abstract: This paper discusses the design of unimodular waveforms with low correlation sidelobes that is useful for MIMO radar. These waveforms can suppress range sidelobes masking and mutual interferences among different echo signals. First, according to the relationship between the aperiodic correlation sequences and the waveforms Power Spectral Density (PSD), the correlation porperty optimization is transformed into the PSD optimization. Then, based on the PSD approximation, the designed waveforms PSDs are approximated to ideal ones. Finally, under the algorithm framework of alternating projection, Fast Fourier Transform (FFT) are used to optimize the waveforms. The numerical simulations demonstrate that the proposed method can design waveforms with good correlations for MIMO radar and it is computationally efficient.