The various luminescent properties of carbon nanodots (CDs) reveal fascinating applications in several areas. Here, bright and multicolor chemiluminescence (CL) is realized from CDs, whose CL quantum yield can be optimized by adjusting the energy level alignment between the CDs and 1,2-dioxetanedione intermediate generated from the reaction of peroxalate and hydrogen peroxide. A CL quantum yield of 9.32 × 10 Einsteins mol, maximal luminance of 3.28 cd m, and lifetime of 186.4 s are achieved in red CDs, all of which are the best values ever reported for CDs. As a proof-of-concept prototype, a high-quality information encryption strategy is established via CD based CL imaging techniques by virtue of the high brightness and multicolor CL.