Designing a multifunctional nanomedicine for integration of precise diagnosis and effective treatment of tumors is desirable but remains a great challenge. Here, we report a multifunctional nanomedicine based on WS2 quantum dots (QDs), which was prepared by a facile and "green" method through physical grinding and ultrasonication. The as-obtained WS2 QDs with small size (3 nm) possess not only significant X-ray computed tomography (CT)/photoaccoustic (PA) imaging signal enhancement but also remarkable photothermal therapy (PTT)/radiotherapy (RT) synergistic effect for tumor treatment. With CT/PA imaging and the synergistic effect between PTT and RT, the tumor could be accurately positioned and thoroughly eradicated in vivo after intravenous injection of WS2 QDs. Moreover, hematoxylin and eosin staining, blood hematology, and biochemistry analysis revealed no noticeable toxicity of WS2 QDs in vitro and in vivo, which confirmed that WS2 QDs possess good biocompatibility. This multifunctional nanoparticle could play an important role in facilitating simultaneously multimodal imaging and synergistic therapy between PTT and RT to achieve better therapeutic efficacy.