The outrush water in tunnel bore hole brings great drilling operation problem to conventional small diameter coring operations. It was found that the core could get out of the hole with the high water pressure inside the hole combined with the drilling operation of the tunnel hole to explore Ia ore body of Shuiyindong Gold Mine. Thus, the core-uplift-coefficient ξ was put forward; its physical meaning is that under the action of water pressure and buoyancy at the bottom of the hole, the core overcomes its gravity and the friction force to automatically rise. And its practical significance was discussed in combination with the practical parameters of bore holes. When ξ is greater than or equal to 1, theoretically the cores at the bottom of the hole can rush out of the hole with the gushing water. When ξ is smaller than 1, the cores cannot rush out of the hole and drillers should pull out the drilling strings to obtain the cores. By calculating the ξ of the ore layer and combining with the integrity of the actual stratum, it helps the drillers to control the proper drill footage to make sure the ξ≥1. So the core in the drill hole can be automatically lift up from the bottom of the hole. The core-uplift-coefficient ξ not only can provide theoretical guidance for the high pressure water hole in the surface or tunnel drilling holes, but also has certain practical significance.