Abstract: An optimization method of thinning multiple-input multiple-output(MIMO) radar arrays based on almost difference sets (ADS) is presented to avoid the shortage in quantity of cyclic difference sets (CDS)-based array configurations caused by the strict construction conditions of CDS. This method can analytically determine the element locations of transmitting and receiving arrays, and a priori estimate the upper bound of virtual array pattern sidelobes. Considering the advantages of better sidelobe performances with respect to random arrays and richer configuration choices with respect to CDS-based MIMO arrays, the proposed method is of common use in antenna engineering. Extensive simulations are performed to verify the effectiveness of the proposed method.