Abstract: Large fragments are chiefly generated at the upside parts of bench in open-pit bench blasting，and this problem isn′t well solved all the time，especially in the hydrous holes.In view of the situation that hydrous holes exist in most of open-pit mines，and in order to reduce rate of block at upside parts of bench in blasting，the charge structure of stiffened water sealing for large diameter holes is presented by analyzing the characteristics of water medium under high-impact and on-site test in Heshangqiao iron ore.That is，a certain length of water column is retained between tamping and explosive，and the stiffened tamping ammunition is arranged between tamping and water column.The theoretical analysis，calculation and on-site tests of the stiffened tamping blasting showed that this blasting technology effectively improved the block composition at upside parts of bench after blasting，reduced the rate of block and increased the utilization efficiency of explosive.By this method，the costs of secondary crushing after blasting is reduced，and the mine productivity is improved as well.Meanwhile，this technique can effectively decrease the blasting dust and create a favorable working environment for staff.Its spreading and application in similar mine achieved good economic and social benefit.

Key words: Hydrated hole, Stiffened water sealing, Stiffened tamping ammunition, Rate of block