In order to expand the application range of casting aluminum alloy ZL105, the stirring fusion casting method was used to add carbon nanotubes (CNTs) with different content and aspect ratio into the ZL105 aluminum matrix. And then the effect of the reinforcement on the mechanical properties of the alloy was compared and analyzed. The research results show that the tensile strength and hardness of the carbon nanotube composites with different contents will be improved, but to a certain extent the elongation of the composite material will be reduced, and there is an optimal addition amount. The mechanical properties of composite materials prepared by adding CNTs with relatively small length and diameter are better. There are different forms of reinforcement mechanisms for CNTs to reinforce cast aluminum alloys, and the improvement of composite material performance is the result of the combined effect of multiple strengthening methods. The research has made a meaningful exploration for the realization of carbon nanotube reinforced aluminum matrix composites under the casting method.