Using carbon nanotubes (CNTs) as reinforced phase, it was made to carbon nanotubes/Magnesium matrix composite by the foundry method in Argon gas protection. The experiment results show that CNTs can strengthen the mechanical properties of the CNTs/Magnesium matrix composite, and tensile strength and elongation ratio are greatly improved. Furthermore, the plating CNTs are better than un-plating CNTs in strengthening effects. Additionally the quantity of CNTs can not be too great, or the properties will be descended to a great extent without distraction of CNTs. Tensile strength has been higher by 150 % and the elongation ratio is higher by 30 % than matrix’s at best, and the fracture of the composite sample has a character of dimples.