The effect of constraint on the void configuration and coalescence are investigated experimentally using the 3-dimensional fracture surface observations under the SEM (Scanning Electron Microscope) and 3dimensional imaging analysis. The constraint effect is analysed by changing the specimen shape. The SiC particle reinforced Al 2025 aluminium alloy composites is used to test the ductile fracture by nucleation, growth and coalescence of micro voids under the different structure of materials and the different constraint conditions. The experimental results show that the void aspect ration is decreased with increases of SiC particle volume fraction in aluminium alloy and the final void volume fraction at fracture also changed by the specimen. The effect of the local constraint effect is analysed by using the 2dimensional FEM analysis. The results shown that the void shape agree with the experimental one qualitatively in different constraint specimens