Located on the western margin of the Yangtze Plate, Emeishan Large Igneous Province (ELIP) has experienced multi-episode tectonic movement since Late Permian, and hence the original spatial distribution of the Emeishan basalt has not been fully preserved. This fact leads to the underestimation of the magnitude of ELIP magmatism. Recently, some seismic tomography studies suggest that ELIP was produced by the delamination of lower crust rather than the mantle plume activity, which is based on the absence of high velocity layer in the ELIP crust. According to the linear relationship between P-wave velocity and density and the P-wave velocity of the crust acquired by Ljiang-Qingzhen seismic profile, the authors estimated the crustal densities of the core and periphery zone of inner belt and those of the middle and outer belts of ELIP. The result reveals significant difference of the crustal density structure between the inner belt and the outer zones of ELIP. Compared with the middle belt of ELIP, the density of the upper crust of the inner belt is about 79 kg/m³ higher, and the densities of the upper and the lower parts of lower crust are 68 kg/m³ and 101 kg/m³ higher, respectively. Compared with the outer belt, the density of upper crust of the inner belt is about 92 kg/m³ higher, and the densities of the upper and the lower parts of lower crust are 99 kg/m³ and 126 kg/m³ higher, respectively. The high density of the crust in the core region of the inner belt resulted from the emplacement and accumulation of mafic-ultramafic plutonic rocks. Based on the crustal density structures of different belts, the total volume of (45~120)×10⁴ km³ was estimated for the high density mafic-ultramafic rocks, which were intruded into the core region of the inner belt. Together with the volume of Emeishan basalt, the magnitude of magmatism of ELIP is up to (0.7~1.8)×10⁶ km³. This result favors the mantle plume origin of the ELIP.