_{:Ti55.5Cu18.5Ni17.5Al8.5amorphous powders were produced by mechanical alloying process. The microstructure, amorphization behavior and hardness were studied by X-ray diffraction, differential scanning calorimetry, scanning electronic microscopy and transmission electron microscopy, et al. The results show that the microstructure changed significantly with increasing milling time. Firstly grain size decreased and nanometric intermetallic appeared. Secondly long range disordered structure occured inside the nanometric intermetallics with further milling. Finally the intermetalics were separated into many smaller parts by the disordered structure and then amorphization. The amorphization mechaniam was stuied at atomic scale and shows that the major reason is the server plastic deformation occurred during high energy ball milling, leading to high density of dislocation and large lattice distortaion, which results into long range disordered structure and amorphous structure. The alloy’s hardness increases significantly with milling owing to the work hardening and amorphization during ball milling.}