Carbon quantum dots (CDs) have been frequently used for broadening spectrum light response due to their superior up-conversion photoluminescence (UPPL) property and effective charge separation capacity. In this study, a novel CDs modified Z-scheme photocatalyst (CDs/g-C3N4/MoO3) was successfully constructed. The morphologies, chemical compositions, and optical properties of the prepared catalysts were investigated via a series of characterization techniques. Systematic studies indicated that the CDs/g-C3N4/MoO3 photocatalyst exhibited remarkably enhanced visible-light photocatalytic activity for the degradation of tetracycline (TC) compared to pristine g-C3N4 and MoO3/g-C3N4 composite. Doping 0.5% CDs resulted in the highest TC degradation rate, which was 3.5 and 46.2 times higher than that of MoO3/g-C3N4 and g-C3N4, respectively. The enhanced photocatalytic performance of CDs/g-C3N4/MoO3 can be attributed to the synergistic effects of CD properties (i.e., excellent UPPL activity and high charge separation capacity and the Z-scheme heterojunction structure). Reactive species scavenging experiments revealed that photogenerated holes are the main active species during the photocatalytic process. Possible photocatalytic degradation pathways of TC were proposed through the identification of intermediates using HPLC-MS and the frontier electron density calculation. Experimental results showed that the newly fabricated Z-scheme CDs/g-C3N4/MoO3 is a promising photocatalyst for the removal of TC from the environment.