Self-sealing performance of compacted bentonite is the key to reduce the threat posed by high-level radioactive waste in deep geological repositories to the geological environment and human habitat. However, it will be inevitably affected by the field groundwater chemistry, thus influencing the water retard capacity of the engineering barrier. For this reason, a series of hydration tests with simulated radial technological voids were conducted on compacted bentonite, and the evolutionary process was visualized using a custom-designed device. Effect of groundwater concentration was considered using synthetic water with different total dissolved solids. Results show that the filling of the technological void is actually a free swell process, and the fast increase of crack area coincided with the rapid expansion of the primary swelling. As the salinity increased, the crack development extent decreased in terms of both propagation rate and the maximum crack area and so was the time duration to reach the peak of cracking. However, in the cases of higher salinity, a slower sealing rate and longer sealing period were observed. At the end of the hydration test, the water content decreased as the water salinity increased at all sample locations; the dry densities of the inner and middle sections were larger than that in the outer section. Those observations are of great importance in the evaluation of the self-sealing capacity in the field of water chemistry conditions and thus guide the design of the engineering barrier.