The invention provides a metal mold gravity casting method. After molten metal is cast into a metal mold mould in a gravity mode, an extrusion rod is used for extruding a cavity of the mould downward in a perpendicular mode on the position of a mould pouring cup, so that the molten metal is solidified under pressure and formed in a flowing mode. The solidified metal is deformed in a plastic mode under the pressure, so that the defects such as shrinkage cavities and shrinkage porosities of castings are avoided, organization is compact, mechanical property is improved, dead heads and working allowance are reduced, and a metal use ratio is high.