The invention provides a lightweight UAV shell and a preparation method thereof. The lightweight UAV shell comprises a substrate and a protective layer covering the surface of the substrate. The protective layer comprises a magnetic coating layer, an adhesive layer, a transmission layer, an electromagnetic fiber layer, and a carbon fiber composite layer which are located from the near to the distant from the surface of the substrate. Preferably, the material of the substrate is magnesium aluminum alloy. Preferably, the electromagnetic fiber layer is a grid layer having a plurality of parallelograms and formed by a plurality of staggered electromagnetic functional fibers. Preferably, the electromagnetic functional fibers are electromagnetic functional carbon fibers or electromagnetic functional silicon carbide fibers. Preferably, the carbon fiber composite layer is composed of the following raw materials by weight: 50 parts of resin material, 20-30 parts of reinforcing material, 5-10 parts of filler, and 5-10 parts of auxiliary agent. Preferably, the adhesive layer is formed by cold spraying low-melting-point alloy and has a thickness of 0.1 to 0.2mm. The proportion of the weight ofthe UAV shell to the total weight of whole UAV can be reduced, thereby improving the load capacity and the use performance of the UAV.