One kind of 3DNMMC with different volume fraction reinforcement phase was fabricated by pressureless technique. The bending strength and fracture toughness were tested by 3-P bending strength experiments. When the volume fraction of reinforcement phase phase was not in excess of 10%, composites had an improvement of bending strength and fracture toughness owing to relatively homogeneous Al2O3 particle distribution encircled by metal matrix and the occurrence of interface reaction product as MgAlO2 spinel phase. Much and smaller craters and dimples are observed in metal matrix alloy and limited ductility of composites causes the early failure of composites. With the increases of volume fraction of reinforcement phase phase, crack characteristic consist of crack nucleation, growth, coalescence and crack propagation became the main fracture failure mechanisms.