S1: prefabricating a pile foundation body, wherein the pile foundation body has a columnar structure, and a plurality of extension connection ports are provided at an outer side and a bottom of the pile foundation body; and

S2: digging a foundation pit at a designated monitoring point; combining the pile foundation body with an extension body to form a fixed monitoring pile; placing the fixed monitoring pile into the foundation pit, such that a bottom extension body and a side extension body are inserted into the pit foundation; and backfilling and compacting;

wherein in step S1, the pile foundation body comprises the following components that are combined together through cement pouring: a plurality of steel reinforcement rings, a plurality of side connecting reinforcement bars, a central vertical reinforcement bar, and a plurality of spiral reinforcement tubes; the plurality of steel reinforcement rings are vertically spaced and connected by the plurality of side connecting reinforcement bars; the central vertical reinforcement bar is located at a center of the steel reinforcement ring; the plurality of spiral reinforcement tubes are distributed at the outer side of the pile foundation body; a bottom of the central vertical reinforcement bar is connected to a spiral reinforcement tube; and open ends of the spiral reinforcement tubes form the extension connection ports.