Abstract: Interfacial interactions between fiber reinforcement and soil play an important role in reinforce benefit.Understanding the interfacial mechanical behavior is helpful to apply effectively the fiber reinforcement in geotechnical engineering practice.The objective of the present work is to study the interfacial micro-mechanical behavior of discrete polypropylene fiber reinforced soil.Three soil types(fiber reinforced raw soil, cement soil and lime soil)commonly used in the field were taken into account.The evolution of the interfacial microstructure and fiber surface morphology in these soil types were characterized by using scanning electron microscopy(SEM).It was found that the bond strength between fibers and soil matrix and the associated interfacial friction are the dominant mechanism of fiber reinforced soil.They seem to be controlled by the soil properties and interface condition(microstructure, soil composition, fiber surface roughness etc.).In fiber reinforced raw soil, the fiber surface is attached by many clay minerals.In fiber reinforced cement soil, the interfacial bond strength plays a main role in the interfacial mechanical behavior.In fiber reinforced lime soil, evident plastic deformation is observed on fiber surface, which greatly improved the interfacial friction.