In this article, an adaptive multiscale algorithm is presented for the analysis of scattering by a thin, perfectly conducting plate. This algorithm employs the conventional moment method and a special matrix transformation, which is derived from solving the first-kind Fredholm equation of the first-kind by the multiscale technique. Pulse functions and Dirac delta functions are used for expansion and testing functions, respectively, utilizing the conventional moment method. The impedance matrix and the source terms of the matrix equation are computed using a five-point average scheme. By use of the matrix transformation, the currents, source terms and impedance matrix can be arranged in the form of different scales resulting in an adaptive multiscale method. By going from one scale to another scale, the initial estimate for the solution can be predicted according to the properties of the multiscale technique. AMMM can reduce automatically the size of the linear equations so as to improve the efficiency of the conventional moment method. Several numerical results are presented, which demonstrate that AMMM is a useful method to analyze the scattering from perfectly conducting plates.