Abstract: The transmit beampattern methods available for the MIMO radar can not be extended into the planer array MIMO radar. With the application of the base-beam and probability selecting methods, an approach to design the transmit beampattern for the planer array MIMO radar is presented in this paper, which is based on the idea that the beampattern of planer array can be synthetised by the beampattern of a horizontal and vertical line array. First, the desired beampattern is accumulated along the azimuth and consequently the 1-D beampattern along the elevation can be formed. The elevation base-beam collection of the vertical line array and the corresponding probability selecting optimization model are formulated. Then, the azimuth base-beam collection of the horizontal line array and the corresponding probability selecting optimization model can also be formulated for the desired azimuth beampattern of a candidate elevation. Finally, the 2-D base-beam collection is synthetised and the corresponding selected probability of the collection elements can be calculated. Consequently, the transmit beampattern and the transmit signal can be well obtained using the convex optimization approaches.