To meet the demand for green construction of power grids in the new era, it is urgent to develop and apply a new type of environment-friendly foundation for power grid projects. For this purpose, an improved thin-walled tapered-end grouted miniature steel pipe pile was proposed, and the uplift bearing characteristics of this pile were studied through field tests. With the project background of the 220 kV line Shuanglou-Jiaohe Dongguang north substation, 18 steel pipe piles with two pile diameters of 159 mm and 203 mm, two burial depths of 5 m and 8 m were designed under two conditions of grouting and no grouting. The effects of grouting on the load–displacement curves, uplift bearing capacities, and soil failure modes for different test piles were analyzed through on-site uplift bearing characteristic tests. Based on the failure mechanism of pile–soil interface obtained through the field tests, a finite element model incorporated the pile–soil interaction for the tests was established, and the uplift deformation and failure process of the steel pipe pile was numerically simulated and analyzed. The simulation results showed that the failure modes of the pile–soil interface were consistent with the field tests. By comparing the shear strength parameters and microstructure of the soil around the pile before and after grouting, the macroscopic and microscopic mechanism of the influence of grouting on the soil around the pile was analyzed. The test results are as follows: 1) The load–displacement curve of steel pipe pile changed from steep drop type to slow change type after grouting, and the grouting enhanced the ability of the pile foundation to resist plastic deformation. 2) The uplift capacity of steel pipe pile increased by 59%～148% after grouting, and the increase range was negatively related to the slenderness ratio of test pile. 3) There were few cracks in the surface soil at the failure state of uplift tests for the non-grouting steel pipe piles. The pile body was almost extracted, and the surface soil appeared radial and circumferential cracks at the failure state of the grouting steel pipe piles. 4) Many voids in soil were filled in the process of grouting, which improved the soil strength around the pile. Cement consolidation was formed around the steel pipe pile after grouting, and a shear surface was formed between the cement consolidation and soil. This conclusion was also supported by the numerical simulation results. The influence mechanism of grouting on the uplift bearing capacity of steel pipe pile was mainly reflected in the increase of shear area and side friction of soil around the pile. The engineering application showed that the proposed steel pipe pile had a short construction period, a high bearing capacity, and a low impact on the surrounding environment. These steel pipe piles have been well popularized and applied in the 220 kV line project Shuanglou-Jiaohe Dongguang north substation.