The development of efficient contrast agents for tumor-targeted imaging remains a critical challenge in the clinic. Herein, we proposed a tumor-derived extracellular vesicle (EV)-mediated targeting approach to improve in vivo tumor imaging using ternary downconversion nanoparticles (DCNPs) with strong near infrared II (NIR-II) luminescence at 1,525 nm. The EVs were metabolically engineered with azide group, followed by in vivo labeling of DCNPs through copper-free click chemistry. By taking advantage of the homologous targeting property of tumor derived EVs, remarkable improvement in the tumor accumulation (6.5% injection dose (ID)/g) was achieved in the subcutaneous colorectal cancer model when compared to that of individual DCNPs via passive targeting (1.1% ID/g). Importantly, such bioorthogonal labeling significantly increased NIR-II luminescence signals and prolonged the retention at tumor sites. Our work demonstrates the great potential of EVs-mediated bioorthogonal approach for in vivo labeling of NIR-II optical probes, which provides a robust tool for tumor-specific imaging and targeted therapy.