In the present work, a structure-dependent ratiometric fluorescence (RF) sensor constructed with boric acid–modified carbon quantum dots (B-CQDs) and Tb-MOF(MOF-76) was developed for sensing 2,6-pyridinedicarboxylic acid (DPA). Based on the distinct fluorescent responses of B-CQDs and MOF-76 to DPA, MOF-76/B-CQDs can be developed as a RF sensor for DPA detection. In this RF sensor, the reticulated cross-linked structure of MOF-76/B-CQDs can be destroyed by DPA due to a strong coordination effect between DPA and the Tb of MOF-76, resulting in the quenching of the fluorescence of B-CQD and the restoration of the fluorescence of MOF-76 after the addition of DPA. Benefiting from the confinement effect of the special structure change, the presented sensor showed high sensitivity toward DPA with a detection limit of 3.05 μM and excellent selectivity over the monochromatic fluorescence sensor. Graphical abstract