To solve the problem of poor performance of Space-Time Adaptive Processing (STAP) based on Multiple-Input Multiple-Output (MIMO) radar in complex environment, a method for joint optimization of transmitting the waveform and receiving the weight is proposed to improve the performance of MIMO-STAP detection.After building the MIMO-STAP model, according to the criterion of maximizing the output Signal to Interference plus Noise Ratio (SINR), the joint optimization of transmitting the waveform and receiving the weight is constructed under the constraints of the property of constant modulus of the transmitted waveforms, clutter suppression, and sidelobe reduction to maximize the output SINR, so that the detection performance of MIMO-STAP can be enhanced.To tackle the obtained sophisticated nonlinear issue, an iterative algorithm is proposed.Each step of the proposed algorithm can be transformed into a Semi-Definite Programming (SDP) problem, and hence it can be solved in an efficient way.Numerical simulations have proved that:Compared with the method only considering clutter suppression, the one only concerning sidelobe suppression, and uncorrelated waveforms, the proposed algorithm can significantly improve the detection performance of MIMO-STAP.