Peroxidase (POD) Nanozyme-based hydrogen peroxide (H₂O₂) detection is popular, but hardly adapt to high concentration of H₂O₂ owing to narrow linear range (LR) and low LR maximum. Here, a solution of combining POD and catalase (CAT) is raised to expand the LR of H₂O₂ assay via decomposing part of H₂O₂. As a proof of concept, a cascade enzyme system (rGRC) is constructed by integrating ruthenium nanoparticles (RuNPs), CAT and graphene together. The rGRC-based sensor does perform an expanded LR and higher LR maximum for H₂O₂ detection. Meanwhile, it is confirmed that LR expansion is closely associated with apparent K_m of rGRC, which is determined by the relative enzyme activity between CAT and POD both in theory and in experiment. At last, rGRC is successfully used to detect high concentration of H₂O₂ (up to 10 mm) in contact lens care solution, which performs higher assay accuracy (close to 100% recovery at 10 mm of H₂O₂) than traditional POD nanozymes. This study brings up a kind of POD/CAT cascade enzyme system and provides a new concept for accurate and facile H₂O₂ detection. Additionally, it replenishes a new enzyme-substrate model of achieving the same pattern with competitive inhibition in enzyme reactions.