Current cancer therapy is seriously challenged by tumor metastasis and recurrence. One promising solution to these problems is to build antitumor immunity. However, immunotherapeutic efficacy is highly impeded by the immunosuppressive state of the tumors. Here a new strategy is presented, catalytic immunotherapy based on artificial enzymes. Cu2−xTe nanoparticles exhibit tunable enzyme‐mimicking activity (including glutathione oxidase and peroxidase) under near‐infrared‐II (NIR‐II) light. The cascade reactions catalyzed by the Cu2−xTe artificial enzyme gradually elevates intratumor oxidative stress to induce immunogenic cell death. Meanwhile, the continuously generated oxidative stress by the Cu2−xTe artificial enzyme reverses the immunosuppressive tumor microenvironment, and boosts antitumor immune responses to eradicate both primary and distant metastatic tumors. Moreover, immunological memory effect is successfully acquired after treatment with the Cu2−xTe artificial enzyme to suppress tumor relapse. Stressed out: Cu2−xTe nanoparticles are presented as a new artificial multienzyme with enzymatic activity reinforced by near‐infrared‐II (NIR‐II) light. Cu2−xTe catalyzes cascade reactions continuously and elevates intratumor oxidative stress, which not only eradicates primary tumors, but also reverses the tumor immunosuppressive (cold) state into a proinflammatory (hot) state to combat tumor metastasis and recurrence.