The invention discloses a post-cast strip anti-seepage construction method, a reinforced concrete reinforcing layer is additionally arranged at the bottom of a bottom plate post-cast strip, a water collecting pit is formed in the bottom of the bottom plate post-cast strip, an underground water pressure release pipe is pre-buried at the bottom of the post-cast strip, and the bottom plate post-caststrip construction joint is obliquely arranged. A special-shaped water-stopping steel plate is arranged, and hidden construction is carried out on the post-cast strip concrete of the bottom plate in asegmented mode. The reinforced concrete reinforcing layer is arranged, so that the pressure resistance of the bottom of the bottom plate post-cast strip is enhanced, the double-layer protection withthe post-cast strip cushion layer is formed, and the leakage risk of the post-cast strip is reduced. The water collecting pit and the pressure release pipe are arranged, so that the accumulated watercan be quickly drained out when the post-cast strip is hidden. The pressure relief pipe can release the underground water pressure in advance to prevent the bottom of the post-cast strip from being damaged. The special-shaped water-stopping steel plate is arranged, so that concrete at the construction joint is subjected to 100% scabbling and the leakage risk of the construction joint is reduced. Through adopting of the construction scheme of the bottom plate post-cast strip concrete sequence hiding in a segmented mode, the risk of transverse cracks due to too long one-time pouring of concreteis effectively avoided.