Abstract:Recently some scholars think that in the crust the stress probably causes slow plastic deformation wave, and consider that this deformation wave is significant in process of earthquake pregnancy, However, it is difficult to observe this deformation wave both in nature and in laboratory. We proceeded some field tests of large Scale samples to explore the existence of this wave. The tests were proceeded in rock body of fault zone. The test bodies of which size is 50×60×30cm8, were made in tunnels, The frictional surface is layer of nature fault gouge. The tests show that during loading the yield time of gouge is not identical. The gouge near the loading end yields first, then the yield scope expands progressively. This process corresponds with the propagation of plastic deformation wave in fault gouge. The measured velocity of plastic deformation wave is about 2-3cm/min, it corresponds to 10-16km/year.