Abstract: In Through-the Wall Imaging (TWI), wall reflections are often stronger than the target, hence they make great interference on the imaging and detection of the target. Spatial filtering based on single input and single output is a traditional method for wall-clutter mitigation, whereas it is not applicable to MIMO Through-the-Wall Radar (TWR). In this paper, the spatial signatures of wall and target from MIMO TWR measurements are analyzed respectively. The results based on parametric models show that the wall reflections not only have no relations with positions of antenna array, but also have symmetry properties, whereas the target reflections do not. According to the above difference, a new method called symmetry subtraction for suppressing wall reflections is introduced. Simulation results indicate that the proposed method can suppress efficiently the wall reflections without affecting target signal.