Constructing robust enzyme mimics capable of disrupting cellular nicotinamide adenine dinucleotide (NAD) homeostasis, such as NADH oxidase (NOX) nanozymes, is emerging as a novel and powerful means to treat cancer. However, owing to the tumor heterogeneity, NOX nanozymes exhibit the different sensitivities toward hypoxic and normoxic cancer cells inside solid tumors, which pose a severe barrier for achieving high therapeutic efficacy. Herein, we propose an innovative design strategy of NOX nanozymes to simultaneously improve the two half-reactions related to NADH oxidation via metal-defect engineering. Taking advantages of distinctive electronic configuration and deprotonation effect around Cu-defect active sites, Cu_2−xSe nanozymes perform excellent NADH dehydrogenation activity and preferential 4e^- oxygen reduction selectivity, thus decreasing the requirement of O₂ in heterogeneous tumor microenvironment. Such unique NADH consumption action of Cu_2−xSe nanozymes efficiently disrupts metabolic networks of solid tumor and enables enhanced antitumor efficacy, which provides a new insight on the constructing metal-defect active centers in NOX nanozymes.