Abstract: Waveform diversity of MIMO radar provides more degrees of freedom for transmit beam-pattern design.Firstly,a min-max criterion is proposed for optimizing the correlation matrix of the transmit waveforms to solve the problem of lowsidelobe and high-gain transmit beam-pattern design under the uniform elemental power constraint.The constrained optimization problem is then converted into an unconstrained optimization problem,which can be solved by classical iterative algorithm. Simulation results show that the min-max sidelobe optimization method can obtain a transmit beam-pattern with flat sidelobe region and lower sidelobe level. Finally,phase-coded signals are optimized using the cyclic algorithm.The beampattern of designed phase-coded signals matches well with the theoretical results.