Abstract: In this paper, based on the monostatic cylindrical scanning model of the dihedral, we analyze the distribution pattern of odd reflection echoes from dihedrals with different opening angles. By establishing a forward scattering model and determining the exit points that contribute the most to the scattering field at each observation angle, we demonstrate that among various scattering mechanisms within the dihedral angle, specular reflection plays a dominant role. Accordingly, this study focuses solely on the contribution of specular reflection to the scattering field and establishes a one-to-one correspondence between the exit points with stationary phase and the wavefront of the echoes. A high-order boundary scattering transform (HBST) algorithm is proposed to effectively eliminate imaging artifacts caused by multiple reflections. Compared to traditional back-projection algorithms, the HBST algorithm shows significant improvements in computational efficiency and imaging effectiveness. Simulation and experimental results validate the effectiveness of the algorithm.