This paper discusses the mechanism indentifying tectonic setting of source regio n of igneous rocks by the ratios among Th、Ta and Hf. Based on the ratios among Th、Ta and Hf of basalts in typical tectonic setting, we propose a new identifi cation method of tectonic setting of magmatic source region by the ratios among Th、 Ta and Hf. The paper also approaches Th、Ta and Hf Characteristics and the tectonic setting of magmatic source region of Emeishan basalts. It turns out tha t Emeishan basalts is petrogenetically related to mantle plume.