Abstract: For the open-pit to underground mining，the shallow open pit becomes a rainwater catch⁃ ment area，and the caving zone or water-conducting fracture zone formed by the deep ore body caving meth⁃ od has established a good channel for surface water to enter the tunnel system，and the deep ore body water filling conditions have changed，which makes surface water to become the main source of water inflow.Tak⁃ ing a certain copper mine in Heilongjiang Province as an example，the reasonable pit water inflow data is obtained by estimating the rainfall runoff infiltration amount and superimposing the underground water in⁃ flow amount，so as to provide the basis for the layout of the underground drainage system.Seepage channels and rock cushion are adopted to prevent the catchment at the bottom of the open pit from suddenly pouring into the tunnels and threatening the safety of personnel and equipment.

Key words: open-pit to underground mining, water inflow, rainfall runoff infiltration, rock cushion, seepage channel