Osteosarcoma (OS) is a highly aggressive bone malignancy with limited treatment options and frequent chemoresistance. Yanghe Decoction (YHD), a traditional Chinese medicine formula, has demonstrated anti-tumor potential, but its mechanisms in OS remain unclear. In this study, we employed a network pharmacology approach to identify 67 active components and 101 OS-related targets of YHD, with core targets including AKT1, TP53, MAPK14, and CASP3, mainly enriched in the PI3K/AKT and MAPK signaling pathways. Molecular docking confirmed strong binding affinities between representative compounds and these targets. Functional experiments revealed that YHD inhibited OS cell proliferation, migration, and invasion, and promoted apoptosis by elevating intracellular reactive oxygen species levels and inducing mitochondrial dysfunction. Mechanistically, YHD suppressed the PI3K/AKT pathway while activating p38 MAPK signaling. Importantly, YHD enhanced the sensitivity of OS cells to cisplatin, demonstrating a synergistic inhibitory effect in vitro and in an orthotopic OS mouse model. These findings suggest that YHD exerts its anti-osteosarcoma effects via reactive oxygen species-mediated mitochondrial disruption and pathway modulation, and may serve as a promising adjuvant to conventional chemotherapy.