Metal nanocluster has been recently developed as a promising electrochemiluminescence (ECL) emitters due to its unique electronic structure and distinctive optical and electrochemistry properties. However, the low ECL efficiency and high cost are still the serious challenges for metal nanocluster-based ECL emitter. Herein, the self-assembly of 4,6-dimethyl-2-mercaptopyrimidine (DMPM) stabilized copper CuNCs (DMPM-CuNCs) into nanosheets was described in detail for the first time, which significantly strengthening its photoluminescence efficiency from 4.3% to 39.3% and improving its photostability and oxidation stability. Most importantly, the ECL efficiency of self-assembled DMPM-CuNCs (DMPM-CuNCs) was markedly enhanced to 39%, reaching a relative high level of reported metal nanocluster-based ECL emitters. This work propose a simple and effective way to improving inherent ECL performance of CuNCs, providing a new guidance for further development of low-cost and high efficiency ECL emitters.