The effect of porosity on the crack propagation is studied by using the cohesive zone model. Standard mode I fracture test were done by using compact tension specimens with various porosities. Load-load line displacement curves and ${delta}_5$-crack resistance curves for various porosities were obtained from experiments. The cohesive zone model proposed by Xu and Needleman was employed to describe the crack propagation in porous media, and the Gurson model is used for constitutive relation of porous materials. These models were implemented into user subroutines of a finite element program ABAQUS. The fracture mode changes from ductile fracture to brittle fracture as the porosity increases. Numerical calculations agree well with experimental results.