This paper is the result of geological survey engineering. [Objective] A large amount of ~ 100 Ma magmatic rocks are developed in the southeast margin of South China. Shifting to interior of South China, although the period of magmatism has been reported sparingly, they were often related to metal mineralization. Determination of the distribution of magmatism of ~ 100 Ma in the interior of South China would provide a scientific basis for the study of the late Yanshanian tectonic setting, and related ore prospecting and exploration. [Methods] Based on the 1︰50000 regional geological survey and detailed petrographic study, the granites in Qiashui area, which are located near the Chenzhou-Linwu fault in the interior of South China, were divided into five intrusive episodes, including (1) porphyritic coarse-medium-grained amphibole-biotite monzogranite, (2) porphyritic medium-fine-grained amphibole-bearing biotite monzogranite, (3) porphyritic medium-fine-grained biotite monzogranite, (4) medium-fine-grained biotite monzogranite with rare porphyrites and (5) fine-grained biotite syenogranite with rare porphyrites, respectively. Zircon LA-ICP-MS U-Pb dating was carried out systematically for the representative rocks of these intrusions. [Results]U-Pb dating yield ages of the first to fifth intrusive episodes ranges from 102 Ma to 97 Ma, which is at the transition of the Early and Late Cretaceous. [Conclusions] According to comprehensive analysis and comparison of the ~100 Ma magmatic events in the interior and southeast coastal regions of South China, it shows that the geodynamic mechanism of the magmatism of ~100 Ma in the interior of South China might be related to back arc and intracontinental lithospheric extension resulting from Paleo-Pacific plate subduction retreation. It led to reactivation and extension of ancient deep faults such as the Chenzhou Linwu fault, and then the intensive mantle and crust magmatism.