Abstract: The development of nuclear energy on a large scale will produce high level radioactive wastes. It is a concerned problem how to dispose of these wastes safely. The deep geological disposal of the high level radioactive wastes is expected to be a safer disposal method in most countries. Granite (Beishan) and clay were considered as suitable geological disposal media in China and Belgium, respectively. To access and analyze the possibilities of granite and clay as candidate rocks in high level waste geological disposal, it is necessary to determine the speciation and solubility of key radionuclides in rock groundwater, which are the input data of calculating the radioactivity and safety factor of repository. Tc, Np and Th were selected as key radionuclides of geological repository and EQ-CALCS software coupled with HYDRA database was used to calculate and experimentally compare the solubility and speciation of radionuclides in granite and clay groundwater in the paper. The Pourbaix figure of radionuclides under different conditions was obtained and the stable speciation of radionuclides in groundwater was determined. The effects of pH on solubility of key radionuclides in groundwater were studied to indicate the maximum source term concentration of radionuclide concerned in geological repository conditions.