Abstract: With the widespread application of transmission lines in complex terrains, the design and stability of pile foundations in sloping ground have become important research topics in geotechnical engineering. This paper systematically summarizes recent progress in theoretical, experimental, and numerical studies of pile foundations under lateral loads in sloping ground. From the theoretical perspective, elastic foundation theories (particularly the m-method), elastoplastic analysis methods (especially the p-y curve method), wedge theory, and limit analysis methods provided a comprehensive framework for evaluating the lateral bearing capacity of pile foundations in sloping ground. Experimental studies demonstrated the significant impact of slope inclination, pile position, and soil properties on the foundation reaction coefficient (m-value) and bearing capacity. Numerical analyses further quantified the influence of slope geometric parameters and loading conditions on the response of pile foundations, while exploring the degradation mechanisms of pile performance for transmission lines under complex conditions, such as seismic loads, variations in pile diameter, and waste soil backfilling. The findings of this review can provide a theoretical basis and engineering references for the design and optimization of pile foundations for transmission lines in sloping ground, which is significant importance for ensuring the stability of power facilities in mountainous areas.