The invention belongs to the field of subway construction. In order to solve the problem that during urban subway excavation, seepage of an excavated tunnel face affects the construction of a mining project since there are no conditions for precipitation well construction due to surface ambient restraints, the invention provides a construction method of a large-diameter precipitation well in a subway mined tunnel; the method comprises: excavating a precipitation guide hole parallel to a mined tunnel, constructing a large-diameter precipitation well in the precipitation guide hole, discharging accumulated water in the precipitation well to a drain pipe through a water discharge pipeline, an intra-tunnel water collection chamber and a surface collection pit, and mining construction of the tunnel having no seepage at the tunnel face is achieved. The construction scheme focused on precipitation is adopted herein; by reasonably selecting the type of drill rig in connection with the drill rig and related conditions, the guide hole is set; a shaft and a passage space are utilized to make a drill rig lifting scheme; intra-tunnel precipitation and drainage are finally performed; accordingly, precipitation effect is good, and the mining project in the range can be conducted normally.