A method of manufacturing alloy rim for automobile is disclosed. The method comprises the steps of forming elongated extruded alloy straps with a cross-section shape from alloy by an extruding process; cutting the extruded alloy into the required length; placing the cut alloy obtained in (b) onto a mold to form into an arch-shaped edge; cutting the two ends of the edges of the extruded alloy to form into an inclined angle end; placing the extruded alloy of (d) into a device to form the alloy into a round rim; welding the ends of the two joining ends; performing a surface hardening process; furnishing the rim that obtained in (g) with CNC lathe machine.