Abstract: In order to study the frictional characteristics of rock and gouge,test tunnels were excavated,the test samples were made and testing with large scale samples in field were conducted in the limestone body near Yuanan Fault. The direct shear method was used in the experiments. The size of test samples was 506030 cm3. The area of frictional surface between test samples and rock body was 3000 cm2. There were three kinds of frictional surface: natural fault surface,soft intercalation surface,and joint fissure surface. The average of frictional coefficient measured are: (1) Natural fault surface -0.48; (2) Soft intercalation surface -0.41; (3) Joint fissure surface - 0.84. Comparing with test resuets with small scale samples in the laboratory,it is discovered that the frictional coefficient of gouge in the field is near that in the laboratory,and that the frictional coefficient of rock in the field is near that of rough rock in laboratory. Owing to the large area of frictional surface,the time of yield at different points on the frictional surface were distinctly different. Earlier yield on part of the frictional surface can be looked upon as precursor for prediction of the overall in-s.ability.