Abstract: The aim of this paper is to understand the impacts of thermal aging on the mineral composition and microstructure of Gaomiaozi natural sodium bentonite with Beishan groundwater and to broaden the assessment and scope of buffer materials for geological disposal of high-level radioactive waste(HLW).FTIR, XRD and Mössbauer spectra of GMZ sodium bentonite(contain groundwater from Beishan area) heated at 90℃,150℃,170℃,190℃ and 210℃ respectively continue 2 months, 4 months, 6 months, 8 months, 10 months and 12 months have been studied.In addition, the solubility of silicon in groundwater from Beishan area have been tested.The results indicate that, the content of montmorillonite decreases, the content of mica and zeolite increases significantly with the increment of the thermal temperature and time.The concentration of in groundwater increases obviously as the thermal temperature and time increased.There have the tendency that Fe(Ⅱ) transformed to Fe(Ⅲ) in the bentonite after thermal aged.But, the types of mineral and functional groups remain the same.Overall, the mineral composition of GMZ natural sodium bentonite have been varied after thermal aged, further research is needed to comprehend specific situations.