The present invention relates to a large-diameter fine-grain anti-rust aluminum alloy thin-walled tube preparation method, and belongs to the technical field of metal processing. The method comprises: extruding an Al-Mg-based anti-rust aluminum casting billet material by using a large extruding ratio; turning the extruded billet material to remove the defect structure, and carrying out four passes of large deformation cold-rolling, wherein the total processing rate of the cold rolling is 80-90%, surface treatment and intermediate annealing are performed after two passes of the rolling are performed so as to eliminate the processing hardening structure, and then the two passes of the subsequent cold rolling is performed; and finally carrying out surface treatment and finish product annealing on the rolled tube. According to the present invention, the Al-Mg-based anti-rust aluminum structure manufactured by the method is uniform and fine, and has high performance and high precision, the production process is reduced, the production efficiency is improved, the cost is reduced, the processing forming performances such as subsequent bending, productivity, tube end expansion, flattening and the like of the tube and the reliability during the use can be ensured, and the method is suitable for mass production and has significant economic benefits and social benefits.