The invention provides a casting method of an aluminum alloy cast rod. Chemical composition elements of the aluminum alloy cast rod and the structure of a crystallizer are optimized so that when the aluminum alloy cast rod is cast, a temperature adjusting device, the stirring speed and the stirring time can be more accurately controlled through a controller, formability of aluminum alloy melt is guaranteed, meanwhile, uniformity of the internal temperature of the aluminum alloy melt can be guaranteed, the situation that an aluminum alloy dendritic crystal arm is broken into dendritic crystal fragments is effectively reduced, nucleation positions are added, more non-uniform nucleation occurs, the grain refining effect is remarkably generated, then the tendency that cracks are generated on the cast rod is reduced, the casting smelting quality is improved, and the yield is increased. The problems that when a large-size and large-diameter aluminum alloy cast rod is cast, the temperature of aluminum alloy melt is not uniform due to the high casting temperature, consequently, the cooling speeds and the cooling degrees of all parts of the cast rod are different, the cracking tendency exists, and cracks are generated in the cast rod are effectively solved.