In this study, we propose a design method to develop an arc multiple-input multiple-output (MIMO) antenna array based on the equivalent array concept. Further, an arc MIMO antenna array containing 50 transmitters and 60 receivers is designed. The simulation experiment and analysis conducted in the terahertz band denote that the imaging resolution of the arc MIMO array is almost equal to the theoretical limit. When compared with an equivalent array containing 3000 transmitters, the main-lobe widths of both the point spread functions are observed to be almost identical, and the positions of the side lobe peaks and valleys correspond accordingly. Subsequently, the equivalence between the arc MIMO array and the equivalent array can be verified based on the simulation results. When compared with the traditional linear MIMO array, the arc MIMO array exhibits a larger imaging range, and its side gating artifacts are almost completely reduced. These factors are important to obtain better imaging results with respect to the side view of the curved surface imaging targets.