Based on the excellent properties of g-C3N4, co-doped carbon quantum dots (NS-CQDs) were selected to modify it in order to enhance its peroxidase-like activity, and the synthesized NS-CQDs/g-C3N4 nano-enzymes were applied to the detection of common small molecules, such as hydrogen peroxide and glucose, to provide theoretical basis for the construction of g-C3N4 nano-enzymes-based biosensors. FT-IR, SEM, TEM, and other characterization methods determined the composition and morphology of NS-CQDs/g-C3N4. This paper discusses the influence of different morphologies on composites’ catalytic activity. According to the fluorescence spectrum, thecatalytic mechanismfollowsthe hydroxyl radicalmechanism. Under the optimal experimental conditions, the prepared composites were used to detect glucose, and the resultant detection limit of glucose was 1.63 μΜ. The results showed that NS-CQDs/g-C3N4 outperforms most of the nanoenzymes of similar materials, which provides a new idea to broaden its application in nanoenzymes.