The genesis of diffuse and small-volume­­­­­ basalts in the Mongolia Plateau remains debatable. Crustal structure can provide valuable insights into mechanism of intraplate deformation and volcanic activites. This study combined the teleseismic data from all three dense arrays across the Mongolian Plateau to obtain crustal thickness and Vp/Vs ratio maps with the H-κ-c method. The results reveal crustal thickening in the western plateau, which is related to multiphase magmatic underplating. High Vp/Vs ratios in the Hovsgol Rift indicates mafic magma intrusions and ongoing magmatic underplating. In contrast, low Vp/Vs ratios with localized high patches in the Hangay Dome indactes the magmatic underplating has been differentiated and delaminated; the felsic residues in the crust decrease the Vp/Vs ratio, while the mafic magma reservoir beneath the volcano increases the Vp/Vs ratio locally. The multiphase magmatic underplating provides a reasonable explanation for the sustained and still on-going intraplate volcanism in the Mongolia Plateau.