A method for manufacturing a fully-equiaxed crystalline aluminum alloy cast ingot by using additive manufacturing and rapid solidification techniques, comprising: using an apparatus, the apparatus comprising a metal heating mechanism and a negative pressure cooling mechanism, wherein the metal heating mechanism is located above the negative pressure cooling mechanism and is connected to the negative pressure cooling mechanism by a nozzle; and the negative pressure cooling mechanism comprises a vacuum chamber with a gas inlet hole and a gas outlet hole, and a three-dimensional moving ingot mechanism arranged inside the vacuum chamber, wherein the three-dimensional moving ingot mechanism comprises a moving ingot and a two-dimensional moving platform vertically connected to the moving ingot, a water cooling mechanism is arranged outside the moving ingot, and the moving ingot is configured to be driven by a precision motor to be precisely displaced up and down, wherein the metal heating mechanism comprises a crucible, a filter device, and a nozzle baffle sequentially arranged from top to bottom, a heater and a thermal insulating layer are sequentially arranged at an outside of the crucible, and a nozzle heater configured for pre-heating is arranged at an outlet end of the nozzle, wherein the apparatus is used in such a manner that a molten metal is obtained by heating and melting a metal block in the crucible until the metal block is completely melted, wherein the temperature of the molten metal is increased by heating to its melting point and maintained for 0.5-1.5 hours, the vacuum chamber is evacuated and then the vacuum chamber is filled with an appropriate amount of argon gas to make the gas pressure in the vacuum chamber lower than one standard atmosphere to provide a negative pressure environment, the vertical nozzle is subject to a preheating treatment, wherein a preheating temperature is higher than the melting point of the metal therein, a distance between the moving ingot and the outlet of the nozzle, that is a spraying distance is set to be ≤50 cm, and a vertical distance between the contact surface of the moving ingot and the cooling surface is set to be ≤10 cm, the heated molten metal is sprayed through a vertical nozzle onto a surface of the three-dimensionally movable moving ingot in the negative pressure environment, so that the molten metal is condensed instantaneously when in contact with the surface of the moving ingot, a crystalline layer is obtained by a horizontal planar movement of the moving ingot at a moving speed v1, wherein the crystalline layer has a thickness of δ, the moving speed v1 is set to be v1≤1000 mm/s, and a pass spacing d is set to be d ≤ 20 mm/pass, and then the moving ingot is downward moved by a distance of δ and the planar movement thereof is repeated to form a new crystalline layer, which are repeated many times to obtain the cast ingot. using an apparatus, the apparatus comprising a metal heating mechanism and a negative pressure cooling mechanism, wherein the metal heating mechanism is located above the negative pressure cooling mechanism and is connected to the negative pressure cooling mechanism by a nozzle; and the negative pressure cooling mechanism comprises a vacuum chamber with a gas inlet hole and a gas outlet hole, and a three-dimensional moving ingot mechanism arranged inside the vacuum chamber, wherein the three-dimensional moving ingot mechanism comprises a moving ingot and a two-dimensional moving platform vertically connected to the moving ingot, a water cooling mechanism is arranged outside the moving ingot, and the moving ingot is configured to be driven by a precision motor to be precisely displaced up and down, wherein the metal heating mechanism comprises a crucible, a filter device, and a nozzle baffle sequentially arranged from top to bottom, a heater and a thermal insulating layer are sequentially arranged at an outside of the crucible, and a nozzle heater configured for pre-heating is arranged at an outlet end of the nozzle, wherein the apparatus is used in such a manner that a molten metal is obtained by heating and melting a metal block in the crucible until the metal block is completely melted, wherein the temperature of the molten metal is increased by heating to its melting point and maintained for 0.5-1.5 hours, the vacuum chamber is evacuated and then the vacuum chamber is filled with an appropriate amount of argon gas to make the gas pressure in the vacuum chamber lower than one standard atmosphere to provide a negative pressure environment, the vertical nozzle is subject to a preheating treatment, wherein a preheating temperature is higher than the melting point of the metal therein, a distance between the moving ingot and the outlet of the nozzle, that is a spraying distance is set to be ≤50 cm, and a vertical distance between the contact surface of the moving ingot and the cooling surface is set to be ≤10 cm, the heated molten metal is sprayed through a vertical nozzle onto a surface of the three-dimensionally movable moving ingot in the negative pressure environment, so that the molten metal is condensed instantaneously when in contact with the surface of the moving ingot, a crystalline layer is obtained by a horizontal planar movement of the moving ingot at a moving speed v1, wherein the crystalline layer has a thickness of δ, the moving speed v1 is set to be v1≤1000 mm/s, and a pass spacing d is set to be d ≤ 20 mm/pass, and then the moving ingot is downward moved by a distance of δ and the planar movement thereof is repeated to form a new crystalline layer, which are repeated many times to obtain the cast ingot.