The debate on the Neoproterozoic tectonic background of the Jiangnan orogen includes the mantle plume—rift model, arc- related model, and plate—rift model. Methods: In this paper, the chemical compositions of clinopyroxene and biotite in Huaihua diabase (~788 Ma), were accurately determined by EPMA and LA- ICP- MS, to restrict the diagenetic tectonic setting in this area. Results: The clinopyroxene in Huaihua diabase can be divided into augite and diopside. According to the clinopyroxene characteristics of then(Ca/Al) ratio (3. 48~7. 15) and high w(Ti/Eu) ratio (> 1500), the Neoproterozoic mantle in the western part of the Jiangnan orogen may have suffered multiple metasomatisms of silicate melt and subduction fluid. The crystallization temperature and pressure of clinopyroxene were estimated by the clinopyroxene isotherm, which shows that the crystallization temperature of pyroxene is 1080~1112 ℃, the crystallization pressure is 0. 3~0. 6 GPa, and the corresponding depth is 9. 1~20. 8 km; while the crystallization temperature of the diopside is 1237~1274 ℃, the crystallization pressure is 1. 0~1. 32 GPa, and the corresponding depth is 31. 8~42. 6 km. Conclusions: Together with the results of clinopyroxene and biotite compositions (Al, Ti, Ca, Na and other elements of clinopyroxene and Mg, Fe and other elements of biotite), parental magma series, and tectonic setting discrimination diagram, we recommend that the sub- alkaline tholeiitic magma came from the top of the upper mantle. And the tholeiitic magma was formed by the crystallization differentiation of intraplate alkaline basaltic magma, which was generated by the partial melting of the asthenosphere mantle. Based on the characteristics of the regional tectonic setting, this paper proposes a three- stage plate—rift model to describe the tectonic setting of the Neoproterozoic western Jiangnan orogen.