Osteosarcoma, a prevalent and aggressive skeletal malignancy, significantly impacts the prognosis of individuals, particularly young patients. Current treatments, including surgery and chemotherapy, often prove inadequate for advanced osteosarcoma with metastasis. This study investigates the role of the METTL3/TGF-β1 signaling axis in promoting osteosarcoma progression by inducing mesenchymal stem cells (MSCs) to differentiate into cancer-associated fibroblasts (CAFs). Utilizing co-culture technology, we demonstrated that osteosarcoma cells secrete TGF-β1, which is crucial for MSC differentiation into CAFs, as evidenced by the increased expression of CAF markers α-SMA, FSP-1, and FAP. Additionally, METTL3 was found to enhance the stability and expression of TGF-β1 mRNA through mA modification, thereby facilitating the differentiation process of MSCs. xenograft experiments further confirmed that the METTL3/TGF-β1 axis significantly promotes tumor growth in osteosarcoma by mediating the differentiation of MSCs into CAFs. These findings provide new insights into the molecular mechanisms underlying osteosarcoma progression and highlight potential therapeutic targets for treating advanced stages of this malignancy.