Abstract: The paper presents a systematic research work to study the erosion mechanism evolution of an equal channel angular extrusion (ECAE) treated Titanium alloy Ti5553 exposed to seawater with quartz sand, and the corresponding failure mode of the alloy. It is found that the erosion mechanism micro-cutting, appearing in the early stage,transformed into impact deformation and then kept time invariant at high impinging angle. ECAE processing and the dispersive α-phase,a characteristic microstructure in Ti5553,had influence on the erosion mechanism evolution and the magnitude of erosion wear. It is the increasing of strength,toughness and ductility of Ti5553 that contributed to the improved slurry erosion resistance.