Abstract: The pre-selected site, a repository of very low-level radioactive waste in Southwest China is taken as the study subject. With the static simulation test, effect of pH in aqueous phase on absorption of U and Pu in the soil is studied. With the software PHREEQC, different form and principal components of groundwater solutions are simulated under different pH. The study shows that, in the aqueous environment, the absorption of the soil for nuclides U and Pu reaches absorption equilibrium in 13 days. The pH value has great influence on the absorption of the soil. The acidic solution has a weak effect, while the alkaline solution has a large effect. U and Pu have certain effect of the chemical form and principal components in aqueous solutions on the absorption of the soil. Compounds of U and Pu with charge are easy to combine with the functional groups of the soil surface, which can strengthen the absorption of the soil and heighten the charge density, beneficial to the absorption.