Abstract: A method is proposed to design a phase-coded signal set for multiple-input multiple-output (MIMO) radar systems. This method is used to optimize the correlation properties and improve the orthogonality of phase-coded signal set through the modified moth-flame optimization algorithm. The modified method introduces a flame-updating mechanism, so that the flame population can not only keep optimal moth positions, but also have the ability of searching for the optimal solution. The fitness function of this algorithm is the sum of autocorrelation peak value and the cross-correlation peak value and the energy of the autocorrelation sidelobe value and cross-correlation value. The simulation results show that the modified moth-flame optimization algorithm effectively improves convergence speed and accuracy. In addition, the phase-coded signal set obtained by the proposed method has a low autocorrelation sidelobe value and cross-correlation value.