Abstract: AZ91D alloy composites reinforced by CNTs and SiC_p were fabricated using stir casting process. The mechanical properties, fractographs and microstructure of the composites were characterized by universal material tester. The results showed that CNTs could refine the grains of the composites and good consistention existed between nickel-plated CNTs and matrix. Compared with the matrix alloy, when the volume fraction of CNTs、SiC_p is 1.1% 、3%, the elastic modulus of composite is 70. 8GPa,improved 57.3%. When the content of SiC_p is certain, elongation of composite materials with content of CNTs increase first increase and then decrease; for nickel-containing CNTs composite only, when 1.1% is volume fraction of CNTs, elongation of composites the maximum, highest value was 13.81 percent, than substrate materials near 60.6%, and the extension of 1.1vol% CNTs/2vol% SiC_p/Mg rate slightly lower than the matrix. When the CNTs concentration must, composite material elongation is reduced with increasing content of SiC_p.