Abstract: China plans to construct a high-level radioactive waste geological repository using bentonite as backfilling material. It is great significance for understanding the effect of colloid on the sorption, diffusion and migration behavior of key radio nuclides in the near field of the repository that effectively extract bentonite colloids formed in the groundwater at the repository condition and measure the various physical and chemical parameters. In this paper, analysis of undisturbed Gaomiaozi bentonite by X-ray diffraction and X-ray fluorescence shows that the content of montmorillonite is about 52% and the main elements are Si and Al. A simplified and optimized soil colloid extraction method was set up. This method was used to extract bentonite colloids and to examine the properties of colloids. Our experimental results indicate that ultrasonic oscillation or boil up dispersion method can obtain bentonite colloids of about 100 nm in a shorter time and with better monodispersity. The zeta potential of the colloids are greater than -60 mV suggesting good stability. Analysis by energy dispersive X-ray spectroscopy shows that the main component of the colloids is SiO₂.