Aiming at the full-wave numerical simulation of the large-scale reflective array antennas (LRFAs), a fast and flexible mesh reconstruction method for LRFAs is presented in this letter, which avoids the construction of computer-aided design (CAD) geometry beforehand. For LRFAs with a large number of similar elements, the whole mesh of the LRFAs is assembled using the existing mesh of sub-array and simple transformation operations. To enforce the equivalent current continuity across adjoint sub-arrays, the Discontinuous Galerkin surface integral equation (DG-SIE) method is adopted. Enhanced by the multilevel fast multipole algorithm (MLFMA), the numerical example of an LRFA with up to 5K elements is carried out, and the accuracy and effectiveness of the proposed method are verified by a comparison of the results.