Crustal deformation and deep metallogenic mechanisms in southeastern (SE) China are still debated. In this study, we applied the receiver function method to measure crustal thickness and Poisson’s ratio for crustal rock using teleseismic data recorded at 207 seismic stations from China Earthquake Administration Network. The results showed that crustal thickness varied from ~27 km in the eastern part to ~43 km in the western part of the study area, with an average crustal thickness of 31 km. The crust is thick in the west and thin in the east. The observed Poisson’s ratio for crustal rock was relatively high in the southern Cathaysia Block (CB), with an average of 0.295, while in the Qinling—Dabie terrane, it was relatively low, with an average of 0.257. In the middle of the Yangtze craton and central east of the CB, Poisson’s ratio for crustal rock varied from 0.257 to 0.286. By comparing Poisson’s ratio of the intrusive deposits with that of igneous rocks in volcanic complexes, we deduced that the metallic mineral system might be associated with orogenic and hydrothermal deposits. These results indicated that multistage magma and mineralization in the study area might be attributed to the tectonic-magma-thermal event. The high Poisson’s ratio for crustal rock in the southeastern margin of the CB and northeastern Upper Yangtze Craton might be related to Mesozoic lower crustal mafic partial melt, which provides an important environment for various magmatic intrusions and metallogenies.