Three kinds of fracture specimens are tested under different constraint conditions. One is 3PB(Three Point Bending) specimen, another is CCT(Center Cracked Tension) specimen, and the third one is called CCB(Center Cracked Bending) specimen. By the SEM (Scanning Electron Microscope) observation, it is shown that the roughness of fracture surface is different from each other largely. They are the effect of constraint condition. The dimple fracture process is simulated by the finite element method using Gurson's constitutive equation, and the crack tip stress fields are obtained. The distributions of stress triaxiality components are qualitatively agree with the experimental results. The J-R curves obtained also qualitatively agree with those of experiments, and the fracture surface roughness is well simulated.