The invention provides a rare earth modified aluminum alloy automotive body plate and a preparation method thereof. The preparation method comprises the steps of firstly, material preparing, secondly,smelting, thirdly, casting, fourthly, homogenizing annealing, fifthly, hot rolling, sixthly, cold rolling, seventhly, finished product sawing, eighthly, solution treatment and ninthly, pre-aging, andthe rare earth modified automotive body aluminum alloy plate containingcerium and ytterbium is obtained. According to the prepared automotive body aluminum alloy plate, it is guaranteed that a general aluminum-magnesium-silicon alloy has various properties, meanwhile, the forming property and the mechanical property are improved, the good anti-aging stability and baking hardening property are achieved, the alloy can meet the material requirement of the automotive body plate, and the alloy is applied to the field of automobile lightweight aluminum alloy preparation.