In the solid backfill mining, gangue solid wastes (GSW) are used as the main filling materials. The void ratio and void structure of GSW filling materials under the loaded compression in the goaf are the key factors that affect the heavy metal ion migration with the mine water. In this paper, the transparency of the internal structure of GSW filling materials was realized by CT scanning experiment and 3D reconstruction technology, and then the spatial-temporal evolution characteristics of void ratio and void structure of GSW filling materials were studied under the loaded compression. The results show that: (a) With the progress of loading process, the connectivity between adjacent voids is getting worse, and closed voids are gradually formed; (b) The void's equivalent diameter is mainly concentrated in the range of 15 mm - 25 mm; (c) The change in the overall void ratio of GSW is mainly caused by the change of large voids, and the change of small voids has slight contribution to the change of the overall void ratio. However, the sharp increase in the number of small voids can reflect the poor connectivity and permeability between the voids. This research is of great significance to further understand the migration mechanism of heavy metal ions in the filled goaf, and protect the groundwater environment. (C) 2020 Elsevier B.V. All rights reserved.