A method of making a well-compacted mold by using a vacuum air flow is provided. In the method, molding sand (5) is fed into a space defined by a pattern plate (2) and a flask (3) mounted on the pattern plate (2), and the space is enclosed at the upper part of the flask (3) by a cover (6). The air in the enclosed space is evacuated to reduce the air pressure between the grains of the molding sand in the enclosed space to 1 Torr to 150 Torr, and then air is introduced into the enclosed space from the upper part of the space so that the pressure in the space can increase at the rate of 15 atm/s to compress the molding sand (5). The method eliminates the need for vent holes and enables the mold to be crack-free since the air flow is not reflected.