An efficient single-dye NIR-II CL system was proposed for the first time with the longest emission peak around 1000 nm. Biocompatible CL nanoparticles were developed and a surprising CL intensity enhancement was found in the presence of the BASZn nanoenzyme by about three orders of magnitude. Such an NIR-II CL system was demonstrated for glucose sensing, tumor therapy and in vivo H2O2 imaging. Via theoretical and experimental analyses, a novel electron transfer model was established for such a chemiluminescence system rather than the generally considered HOMODye-LUMODOD model. These findings provide useful guidelines for designing efficient single-dye NIR-II CL systems.