Abstract: In this paper, the linear expansion coefficient and thermal cycling curve of three kinds of high volume fraction SiC_P /Al matrix composites fabricated by vacuum assisted gas pressure infiltration casting were tested at 0～400℃ temperature interval. The results show that the linear expansion coefficient of composites is about half the value of its matrix. The composites' thermal cycling curve is obviously different from that of its matrix. Thermal cycling curves of three composites are also different from each other. It is explained by the theory of plastic strain in matrix. It was found that closing characteristic of thermal cycling curve for composite can be optimized by changing its matrix.