In practical applications, fracture properties and fracture toughness of porous metal foam for bearing are very important. Based on ASTM standards, three-point bending of aluminum foam samples was used to determine I type fracture toughness. It is shown that the fracture of metal foam is brittle fracture. The deformation is localized in the thinnest regions of the cell walls surrounding the crack tip. With further loading, some cell walls existed fracture phenomenon and microcracks appear in the vicinity of the crack tip. With the increasing of load a main crack is initiated at the notch root or at the pre-crack by a coalescence of microcracks, and starts to propagate through the cell structure. The crack follows the weakest path through the structure and creates the secondary cracks and crack bridges. The main way of crack extension is I type fracture. According to the P-V curve characteristics, taking the force and displacement of the maximum load point to calculate the critical crack tip opening displacement, the average cracktip opening displacement is 0.051mm.