The development of highly efficient photocatalysts with broad spectrum light response is a primary goal in the photocatalysis domain. Here we report on a novel ternary photocatalyst comprised of single atom-dispersed silver and carbon quantum dots, co-loaded with ultrathin g-C3N4 (SDAg-CQDs/UCN), which exhibited a highly enhanced photoresponse and broad-spectrum (UV, visible, and near-infrared light) photocatalytic activity. The content of 1.0 wt% of CQDs and 3.0 wt% of Ag resulted in a 10-fold higher reaction rate than that of UCN under visible light irradiation. This improved broad-spectrum photocatalytic performance may be attributed to the surface plasmon resonance effect of Ag, up-converted fluorescent properties of CQDs, narrowed energy gap, as well as the electron separation and transfer capacity of both the Ag and CQDs. An electron spin resonance (ESR) technique, and reactive species (RS) scavenging experiments indicated that O-1(2) and O-2(center dot-) were the dominant active species involved in the degradation of naproxen (NPX). Product identification and reaction site prediction revealed that the photocatalytic degradation of NPX included decarboxylation, hydroxylation, as well as the opening of the naphthalene ring. Mineralization experiments indicated that NPX and its degradation products would be finally transformed into CO2 and H2O. Reactions in different water matrices indicated that SDAg-CQDs/UCN can be effectively employed for the degradation of NPX under ambient water conditions. Therefore, SDAg-CQDs/UCN offers a new strategy for the broad-spectrum utilization of solar light and provides a promising method for the remediation of water contamination.