Post-grouting micro steel pipe pile has the advantages of fast construction speed, flexible layout and high bearing capacity, so it has a broad application prospect in transmission line foundation engineering. At present, the mechanical behavior and strength characteristics of pile-soil interface after grouting have not been quantitatively recognized. Therefore, it is necessary to carry out the experimental research on the mechanical properties and microstructure at pile-soil interface of post-grouting micro steel pipe piles. Relying on Cangzhou Dongguangbei substation 220kV line project to carry out on-site sampling of undisturbed soil and soil at different horizontal distances from the side of non grouting steel pipe pile and post grouting steel pipe pile and the pile-soil interface. The effects of grouting on deformation and shear strength parameters of soil samples were analyzed through laboratory tests. With the help of micro-CT scanner and scanning electron microscope(SEM) testing mrthods, the changes of pile-soil interface structure under grouting and the degree and distribution characteristics of slurry entering undisturbed soil were compared and analyzed. The results show that the infiltration of the slurry after grouting makes the soil structure more compact and the cohesion significantly increased, but the range of influence of the slurry is limited. The research results can provide reference basis for revealing the mechanism of the pile-type reinforcement and the engineering design.