Abstract: In this study, a dry bentonite powder was selected as a sealing material to backfill the joint area between the compacted bentonite-sand blocks. The swelling property of the block system after backfilling was studied considering the initial dry density of blocks as the basic variable. During the swelling test, the swelling stresses at radial and axial direction were monitored in a constant volume condition. The test results show that the swelling stress develops preferentially to the joint area, and the radial swelling stress develops faster than that on the axial direction, which contributes to the sealing of the joint. The final swelling stress in the joint area of the block system increases with the initial dry density of the block, the time to reach the maximum swelling stress shortens, and the healing speed of the joint area improves under the same sealing condition. The swelling deformation of block develops preferentially to the joint area and fills the pores in the joint area resulting in the phenomenon of "stress compensation" that the final axial stresses of blocks decrease. The lower the dry density of the block, the more stress compensation is needed. According to the axial stress curve of the block, the development process of axial stress of block can be divided into three stages: rapid-growth stage, steady-development stage and stress-adjustment stage. The rapid development stage is mainly controlled by the initial dry density of the block, while the steady growth stage is more affected by water migration, side wall friction and the sealing rate of joint. Compared with the intact block, the stress distribution of block with backfilled joint tends to be isotropic, which improves the homogenization degree of the whole barrier system.