The invention provides a preparation technology of an Al-Mg-Si-Cu alloy bar. The preparation technology comprises the following steps of homogenization treatment, saw cutting, three-stage heating, thermal stripping, extrusion, quenching, stretcher straightening, cold-drawing treatment and artificial aging treatment. By reasonably controlling the technological steps and setting parameters, the Al-Mg-Si-Cu alloy bar with both the high tensile strength and the high elongation is prepared. According to the bar, the tensile strength is greater than 310 MPa, and the elongation is greater than 18%. The bar has quite excellent flanging and CNC machining performance, and the typical problems that that 6061-T6 aluminum alloy is insufficient in mechanical performance such as the tensile strength andthe extension strength, and consequentially, fracturing, rough surfaces and the like in the machining process are prone to being caused are solved.