The invention discloses a semi-closed mud pressure maintaining and circulation technique in confined water stratum drilling construction. (A) A drilling machine, a mud pit, a mud pump, an orifice sealing device and a solid-liquid separation device are separately installed; (B) a mud outlet of the mud pit is communicated with a mud inlet of the mud pump and a mud outlet of the mud pump is communicated with a mud inlet of the drilling machine; (C) a mud inlet of the solid-liquid separation device is communicated with a mud outlet of the orifice sealing device and a mud outlet of the solid-liquid separation device is communicated with a mud inlet of the mud pit; (D) according to pressure of the confined water in the drilling position and a pressure threshold value in the solid-liquid separation device with a stratum depth set, a pressure balance between mud in the drilling and water and soil on the stratum is formed; (E) a drill stem of the drilling machine performs drilling construction through the orifice sealing device. The semi-closed mud pressure maintaining and circulation technique in confined water stratum drilling construction does not only cause water and soil loss but also affect the normal propelling of drilling under the protection of the mud.