Abstract: To address the problem that the imaging quality is degraded by the cross-correlation noise caused by coupling among these coded orthogonal waveforms occupied the same frequency in multiple-input and multiple-output synthesis aperture radar（MIMO-SAR），a novel method，i.e.receiving filter based on instrumental variable（IV）is proposed in the paper，which is used to lower the sidelobe level via mismatch processing in the range and decrease the unwanted influence on the imaging caused by the coupling among waveforms.Furthermore，the performance is analyzed quantitatively based on two proposed indexes，i.e，sidelobe level inhibiting factor（SLIF）and synthetic integrated sidelobe level rate improved factor（SISLRIF）.Finally，numerical experiments are provided to demonstrate the effectiveness of the proposed method and it is found that the level of SLIF can reach about 10 dB while maximum value of SISLRIF is nearly 2.5 dB.