Abstract: In order to check the grouting and backfill effects in the overburden strata and mining goaf under ultra thick igneous rock in Haizi Mine and to evaluate th e support effect of the grouting and backfill to the igneous rock, a study on the borehole drilling exploration was conducted in a mining goaf with grouting and backfill co mpleted. The results showed that there were several grouting and backfill layers existed between the mining goaf and the floor interface of the ultra thick igneous rock, t he total thickness of the backfill was 1. 67 m and was taken 72. 6% of the seam mining thickness. In combination with the calculations on the surface ground subsidenc e, the mining height of the seam, the thickness of the backfill mass and others, a residual space height in the strata was only 0.10 m after the grouting and backfill com pleted and the space was backfilled by the broken and swelled rocks in the falling zone. Thus the bed separations of the overburden strata and the voids of the mining goaf were fully backilled and compacted and the grouting and backfill played a support role to the ultra thick igneous rock.