Abstract: The methods of pressureless infiltration in air was employed for fabricating SiCp/Al composite.A series of sample,including different matrix(pure Aluminum.ZL101,ZL301),different particle granularity(70#,100#,150#)and different particle shape(irregular polygon and similar sphere),were fabricated by pressureless infiltration.Mothods:Through determining the coefficient of thermal expansion,which was used to analyse coefficient of thermal expansion of SiCp/Al decreased with increase of SiC particle size.The coefficient of thermal with expansion of composites by similar sphere reinforcement was smaller than that of composite by irregular polygon reinforcement and increase according to such orders as ZL101,pure aluminum,Zl301.