Abstract: When the bag-type filling mining with ultra high water material is used,the filler is easy to be broken down towards rib during the underhand mining stage due to the impact of tilt role at working face. In order to overcome this problem，taking the No. 813 filling face of Shanxi Dazhuang Coal Mine as the research object，the reasons for instability of the filling body are analyzed with brief mechanical model，and the stability controlling method is proposed: adjusting the ratio of super high water，and strengthening the support of filling body. The first successful application of the underhand mining filling with super high-water material shows that the super high water material is a filling material with good performance which can overcome the instability problems of filling body in underhand mining conditions.

Key words: Underhand mining, Super high-water material, Bag-type filling, Filler, Stability