The invention belongs to a casting technology for an aluminum-magnesium-manganese alloy with high plasticity, tenacity and strength. The casting technology is characterized by adopting the following steps that a, smelting is conducted in a resistance reflecting furnace (1) of 300 kg, then the resistance reflecting furnace (1) is inflated with argon, and refining is conducted for 3 min; b, cold rolling is conducted, and an aluminum ingot with the thickness of 25 mm at the normal temperature is placed in a cold rolling machine (2) to be subjected to cold rolling; c, annealing is conducted, a sectional material is placed in a moderate oven (3), the sectional material is heated along with the moderate oven (3), the temperature is increased to 200 DEG C, 300 DEG C, 400 DEG C and 500 DEG C sequentially, and after 60 min is kept, natural cooling in air is conducted to the normal temperature; d, structure observing and sample machining are conducted; e, structure observation is conducted, a prepared aluminum alloy sectional material sample is placed under a PhillipsCM-12 transmission electron microscope (5), and a microstructure of the aluminum alloy is observed; and f, the tensile test is conducted. According to the casting technology, the plasticity, tenacity and stress corrosion resistance of the aluminum-magnesium-manganese alloy is greatly improved, and high-quality metal materials are provided for automobiles, airplanes and space equipment.