The utility model relates to a vertical buried pipe suitable for underground drilling non-pressure pipe descending of a deep foundation pit ground source heat pump system. wherein the length of the vertical buried pipe base pipe is consistent with the depth of an effective heat exchange section, the U-shaped pipe connector is composed of a middle U-shaped bent pipe, a left short connecting pipe, aright short connecting pipe and a flat clamping protrusion provided with a limiting hole, and the marking rope is provided with a lower pipe depth mark and a pipe finding mark. During assembly, one ends of the vertical buried pipe base pipes are connected through the U-shaped pipe joints to form an open U-shaped vertical buried pipe; the other ends of the U-shaped vertical buried pipes are connected with one another through U-shaped pipe joints to form a closed-loop U-shaped vertical buried pipe without pressure after the pipe is filled with water; one end of the marking rope is fixedly arranged on the limiting hole of the U-shaped pipe joint; the closed-loop U-shaped vertical buried pipe automatically falls to a target section under the guidance of a drill rod well hole and the guidanceof upper and lower pipe depth marks of the marking rope by means of the gravity of the closed-loop U-shaped vertical buried pipe, and the closed-loop U-shaped vertical buried pipe is simple and reasonable in structure, convenient to construct, efficient, small in material consumption, free of waste and high in practicability.