In order to accurately find out the geological conditions along the tunnel， horizontal wireline core drilling technology is usually used； however， it is difficult to run drilling tools and fishing tools in ultra-deep water gushing horizontal holes in wireline core drilling. Research was carried out to solve the problem from several aspects， including developing special horizontal drilling rig， selecting the high-power mud pump， sealing off and diverting water gushing， designing the wireline feeder for the wireline drilling tool， custom-making special inner-flush horizontal drilling wireline coring drill rods. The influence factors such as mud pump pressure， drill rod inner diameter size， drilling depth， drill rod water-tightness， drilling water gushing volume， water gushing pressure， borehole annulus， on the speed of running the drilling tools and lifting the fishing gear are comprehensively analyzed. With careful organization， a horizontal hole with large gushing water at the 1000m depth level was successfully completed with wireline core drilling， and with high efficiency and low cost. It also accurately identified the engineering geological conditions along the tunnel， achieving satisfactory technical results. It can provide safety guarantee for tunnel design and construction， and also provide valuable experience for drilling horizontal holes with ultra-deep water gushing.