5052/AZ31/5052 tri-layer clad sheet is a new material with energy saving and consumption reduction. It is of vital significance to study its formibility for its wide applications in industrial field. The forming limit curves of 5052Al/AZ31Mg/5052Al tri-layer clad sheet at 170℃ and 230℃ were obtained respectively by using hemispherical punch. Fracture morphology at limit position and the interface diffusion behavior during bulging process were studied. The results showed that: 5052Al/AZ31Mg/5052Al tri-layer clad sheet has a superior formability at 230℃; the bulging process promoted magnesium and aluminum elements near the bond interface distributed homogeneously and had little effect on the thickness of diffusion layer; the defects were eliminated and the mechanical occlusion areas of bond interface were increased by the bulging process, which is beneficial to improve the bond strength of the interface.