The geological condition of host rock is complicated and a wider fissure cross over at -185m crosscut for new south airshaft in Tonglushan Mine. The arch and walls of crosscut was primary supported with concrete lining. But during the pressing water test before grouting against water at the water outlet, it was founded that a great deal of water leaks happened in the supported zone. And then a backwall injection was applied to the zone with a satisfactory result.