Magmatic underplating is an important process in the interaction between the crust and mantle and for un-derstanding continental accretion. However, identification of underplating process is a very difficult task. Based on seismic, geothermal and geoelectrical data collected during the site-selection investigations for the Chinese continental scientific drilling project, it is inferred that an event of magmatic underplating occurred accompany-ing the Jiashan-Xiangshui continental rift system in the Eogene Period. This magmatic underplating process had the same heat origin with the rift system. The thickness of the transition zone between the crust and the mantle is about 3 km and composition of the zone might be the interbed of peridotite and basic granulites. To-gether with the data of basalts in the area, it is estimated that the average rate of vertical thickening of the con-tinental crust owing to the magmatic underplating is about 0. 1 mm/year.