The design of highly efficient catalysts for the cleavage of various lignin linkages is the key step in the depolymerization of lignin. In this paper, strong-base-modified covalent triazine frameworks (CTFs) were reported to be effective in the cleavage of the β-O-4 linkage. With the modification, the cleavage rate of the β-O-4 linkage was enhanced remarkably. Insight into the catalytic mechanism illustrated that the strong basic sites assisted the activation of Cβ–H bonds, which accounted for the promotion effect. The catalyst was further applied to the depolymerization of organosolv lignin, which showed 87% conversion of the β-O-4 linkage. This strategy should be useful in the catalyst design for lignin depolymerization.