Although NIR-II laser-mediated photothermal therapy (PTT) is considered as an emerging strategy for tumor therapy, its therapeutic effects are still seriously hampered by low photothermal conversion efficacy, limited tissue penetration depth, and inevitable damage to adjoining healthy tissues. Herein, we report a mild second-near-infrared (NIR-II) photothermal-augmented nanocatalytic therapy (NCT) nanoplatform based on CD@Co3O4 heterojunctions by depositing NIR-II-responsive carbon dots (CDs) onto the surface of Co3O4 nanozymes. The as-prepared Co3O4 nanozymes possess multi-enzyme-mimicking catalytic activity including peroxidase, catalase, and glutathione-peroxidase to realize the cascade amplification of ROS levels owing to the presence of multivalent Co2+ and Co3+. CDs with a high NIR-II photothermal conversion efficiency (PCE) (51.1%) enable the realization of mild PTT (∼43 °C), which could not only avoid damage to adjoining healthy tissues but also enhance the multi-enzyme-mimic catalytic activity of Co3O4 nanozymes. More importantly, the NIR-II photothermal properties of CDs and the multi-enzyme-mimicking catalytic activity of Co3O4 nanozymes are greatly augmented by the fabrication of heterojunctions due to the induced localized surface plasmonic resonance (LSPR) and accelerated carrier transfer. On the basis of these advantages, satisfactory mild PTT-amplified NCT is accomplished. Our work presents a promising approach for mild NIR-II photothermal-amplified NCT based on semiconductor heterojunctions.