The pile foundation project of Xiaohe Bridge on Zhenwu Road in Taiyuan City has a main pier diameter of 2.5m and a design hole depth of 84m. The strata are complex， with a loose powder fine sand lin the upper and a flow plastic silt in the middle. During the construction， problems such as hole collapse， excessive sediment at the bottom of the hole， and difficulty in installing steel reinforcement cages are prone to occur. In response to the technical difficulties encountered by rotary drilling rigs during the construction of large diameter and ultra-deep piles， through careful analysis and exploration， this paper summarized the technical measures taken by rotary drilling rigs in the selection of drilling rigs， preparation of mud， embedding of casing， borehole drilling， production and installation of steel cages， and pouring of underwater concrete during the construction of complex strata. These measures effectively ensured the smooth implementation of the project， ensured construction quality， and improved construction efficiency.