AbstractRecently, artificial photonic structures that exhibit nontrivial topological properties have attracted growing attention due to their capability of achieving one‐way backscatter immune transport of light. While photonic crystals are predominantly employed for achieving nontrivial topologies, effective medium approach based on metamaterials has been recently proposed for realizing topologically protected unidirectional surface states. In this article, a microscopic model to investigate the transmission of topological metamaterial grating is constructed based on the scattering processes involving unidirectional surface states. The numerically simulated transmission efficiency of the grating can be precisely reproduced by the model. The model demonstrates that the sharp transmission resonance of the grating results from the constructive interference of the topologically protected one‐way surface states. The present work provides an intuitive picture for understanding the scattering processes and resonance behaviors of the topologically protected one‐way surface states. Benefitting from the sharp spectral features of the supported resonances, the proposed grating structure may be potentially used for sensing applications.