The essential of rock damage evolution is the deterioration of rock’s meso-structure

which also appears on the surface of rock. The tension tests of limestone samples were employed in the test machine assembled with scanning electronic microscope

and simultaneously the SEM image of sample surface was captured while the sample is being loaded. It is observed that the surface pattern of rock transforms irreversibly and eventually macro cracks appear on the surface due to tension. Moreover the SEM image is analyzed by the method of digital image processing

which includes threshold partition and edge detection

and then the fractal dimension of rock surface is calculated as a parameter to characterize the meso surface pattern of rock. It is concluded that the fractal dimension increases with the increasing of load

and at the same time damage become more severe.