Abstract: The range-ambiguous clutter on the main--beam reduces the estimation accuracy of the real target and leads to a sharp decrease in detection performance, which poses a severe challenge to the traditional radar. Based on the range angle 2D beam pointing of frequency diversity array (FDA)-multiple-input and multiple-output (MIMO) radar, this paper presents a method to countermeasure the main-beam range-ambiguous clutter. This method uses transmitter-receiver airspace to identify ambiguous clutter numbers and based on approximate range of the target being searched, using the multiple signal classification (MUSIC) algorithm to accurately distinguish multiple targets and clutter positions, designing a linearly constrained minimum variance (LCMV) adaptive filter to suppress the mismatched clutter. This method can effectively suppress the main-beam range-ambiguous clutter and improve the performance of target detection in complex environments. Simulation results show the effectiveness of the proposed method.