Abstract: The mechanisms of tensile fracture and strengthening of aluminium alloy matrix composites reinforced with SiC particles are examined. The results show that fracture evolution entails a process of microvoid nucleation, growth, coalescence (MNG) for the PRMMCs and there exhibit three models of initial fracture in the process: toughness fracture of the matrix, boundary separation and particle break. Experimental analyses show that strengthening effect of the composites depends on the matching relations between the matrix and the boundary strength and it is very difficult to strengthen the composites when yield stress of the matrix goes beyound a certain critical value.