Costunolide, a natural germacranolide sesquiterpenoid, exhibits only moderate anti-HCC activity. To enhance its efficacy and tumor selectivity, a series of 37 dimeric costunolide-1,2,3-triazole conjugates was designed and synthesized by integrating dimerization and molecular hybridization strategies. Evaluation of their antiproliferative effects on HepG2, Huh-7, and SK-Hep-1 cells suggested that 25 compounds were more potent than either costunolide or sorafenib. The most active dimer 19 exhibited significant activity with IC₅₀ values of 1.6, 1.3, and 0.7 μmol·L⁻¹, which were 13.1, 14.2, and 34.9-fold greater than those of costunolide. Compound 19 showed favorable selectivity against human normal liver cells (THLE-2) and markedly inhibited colony formation. Through a combination of bioinformatics, docking, and molecular dynamics (MD) simulations, glucose-6-phosphate dehydrogenase (G6PD) was identified as a target of compound 19, which was subsequently validated by DARTS and SPR assays. Functional studies revealed that compound 19 arrested the HCC cell cycle at the G₂/M phase, suppressed migration and invasion by inhibiting epithelial-mesenchymal transition, and triggered both apoptosis and ferroptosis. These findings establish triazole-linked costunolide dimer 19 as a promising lead candidate for the development of novel anti-HCC therapies.