Abstract：The surface strain field evolution of two rock specimens(a marble rectangle column and a marble plate with centre hole) subjected to uniaxial compression，which are observed by digital speckle correlation method，are analyzed. The standard deviation(S) is taken as the characteristics variable of the strain field and the S value of the maximum shear strain field at different loading levels is calculated. It is found that S value is lower and changes slightly during the homogenous deformation stage，where it increases sharply at the heterogeneous deformation stage. According to the variation of S value，the complete deformation and failure process of the two specimens could be divided into five stages. The shear strain fields at typical loading within the five stages are presented；and the deformation field characteristics are concluded. In the first stage，the strain field is homogenous and the loading curve is linear. In the second stage，the slight strain concentration areas or bands appear and the loading curve is slightly curved or continuously keeps linear. The third stage is the strain localization stage，in which several localization bands appear and further are localized. Experimental results show that strain localization of the two specimens in this study begins at a point just before the peak value of the loading curve(99.2% and 92.2% of the peak loads for rectangle column and the centre-holed specimen respectively) and stops at the peak point. The fourth and the fifth stages are at the post-peak of the loading curve，which are the strain softening stage. The localization bands formed in the third stage are interacted and competed in the fourth stage. A final crack appears and the specimen fails along the crack in the fifth stage. Therefore，the deformation of rock after peak value is mainly controlled by the activities of weak bands and macrocracks.
