Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming, the stress concentration and defects such as wrinkling and fracture may easily occur. It is a key to reveal the deformation behaviors in order to obtain a sound product. Based on the ABAQUS platform, a 3D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment. The stress and strain distributions, wall thick-ness variations and bellow profiles of each layer in the whole process, including bulging, folding and springback stages, are studied. Then deformation behaviors of bellows under different forming con-ditions are discussed. It is found that the wall thinning degrees of different layer vary after hydro-forming, and is the largest for the inner layer and smallest for the outer layer. At folding stage, the wall thinning degree of the crown point increases lineally, and the difference among layers increases as the process going. The displacements of the crown point decrease from the inner layer to the outer layer. After springback, the U-shaped cross section changes to a tongue shape, the change of convolution pitch is much larger than the change of convolution height, and the springback val-ues of the inner layer are smaller than the outer layer. An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase. With changing of processparameters, bellows with deep convolution are easily encountered wall thinning during hydroform-ing and convolution distortion after springback. This research is helpful for precision forming of multi-layered bellows.