All-inorganic halide perovskite CsPbBr3 nanocrystals (NCs) have attracted more attention in recent years due to the unique optical feature. To date, most of the research was mainly focused on the photoluminescence (PL) and electrochemiluminescence (ECL) of the perovskite NCs. In this work, the strong chemiluminescence (CL) emission of CsPbBr3 NCs was observed for the first time on the hexane/water interface with the assistance of ammonium persulfate-(NH4)2S2O8 as coreactant. Different coreactants were investigated to demonstrate the effect on the CL behavior and it was found that CL intensity achieved the maximum in the presence of (NH4)2S2O8. In this system, electron transfer took place on the surface of the CsPbBr3 NCs, and the excited CsPbBr3 NCs was originated from the direct chemical oxidation of (NH4)2S2O8. The CL spectrum of CsPbBr3 NCs was also collected and was consistent with their PL and ECL spectra, indicating that CsPbBr3 NCs played a role of luminophor during the CL process. The discovery of monochromatic CL of highly crystallized CsPbBr3 NCs not only extends the applications of halide perovskite materials in the analytical field but also provides a new route for the exploration of the physical chemistry properties.