The invention discloses a solid-liquid separation device under slurry pressure maintaining conditions for confined water stratum drilling construction. The solid-liquid separation device comprises a first pipeline, a second pipeline, a slurry storage tank, an adjustable automatic pressure relief valve and slag storage tanks. An inlet of the first pipeline is communicated with an orifice pipe, and an outlet of the first pipeline is communicated with a lateral inlet of the second pipeline; one end of the second pipeline is connected with a valve, and the other end of the second pipeline is connected with an downward 90-degree elbow; an outlet of the elbow of the second pipeline deeply extends into a cavity of the slurry storage tank and is communicated with an inlet of the slurry storage tank, and the adjustable automatic pressure relief valve is mounted at a slurry outlet in the top of the slurry storage tank; the slag storage tanks are hermetically mounted at slag discharge positions at the bottom of the slurry storage tank via valves. The solid-liquid separation device under the slurry pressure maintaining conditions for the confined water stratum drilling construction has the advantages that the solid-liquid separation device is applied to drilling construction procedures carried out in confined water strata, accordingly, disturbance influence of drilling construction on the original strata can be relieved or prevented by water and soil pressure balance between slurry and the strata, water and soil loss can be reduced, and normal drilling propulsion can be guaranteed.