Abstract: In order to obtain the full field deformation information on the surface of the specimen and near the crack tip during the loading of the rock specimen, the limestone semi-disc specimen containing the prefabricated crack was subjected to a three-point bending test under quasi-static conditions. The digital speckle technique was used to monitor the displacement field and strain field of the sample during the loading and rupture process. The results show that when the sample is in the linear elastic stage, the displacement field is "layered". When the peak load is to be reached, the horizontal displacement field contour will gradually meet at a certain point on the front end of the prefabricated crack, and the vertical displacement field at the front end of the prefabricated crack will be deformed to the maximum. The horizontal strain field is W-shaped at its peak load, and the strain change is the fastest at the tip of the prefabricated crack and the load end. The length of the pre-formed crack has an influence on the intersection of the horizontal displacement field, but has little influence on the vertical displacement field. Compared with the traditional strain gage method, the digital image method is more likely to obtain the crack propagation speed, obtain more full field strain information, and have more advantages in monitoring the rock fracture process and its deformation information.