The precursors-the gestation process and the signal of impending earthquake of the Indian Ocean Earthquake of Ms 8-7 are recorded,with a serious of specially made monitoring instruments,including instruments for stress,resonance,tilt and earth potential.The recordings show that there are great differences for the stress in crust between before and after the eart hquake of Ms 8-7 and that of Ms 8-5. This fact indicates the essential distinction regarding to the formation of these two earthquakes.The causation of the tsunami is analyzed.The sign of underground material migration is also found in the gestation process of Ms 8-7 earthquake.