A magnesium alloy substitution design for an automotive seat back frame is carried out. With the magnesium extrusion profiles and the stamping panel integrated, the weight of the seat back frame is reduced by 41.3% and the lightweight goal is achieved. At the same time, the magnesium alloy stamping panel is processed warm forming analysis and verified the formability of the magnesium alloy panel. Numerical calculations comparing the original structure and the substitution design are performed with finite element software, which ensured that the performance indicators such as the mode, the strength and the stiffness defined by related regulatory requirements are all realized. At last, a magnesium alloy substitution design has been proved to be successful.