Abstract: Disclosed are a soft bistable magnetic actuator, a fabrication method thereof, a fatigue testing device, and an auto underwater vehicle. The method for fabricating the soft bistable magnetic actuator includes the following operations: casting a soft precursor by injection molding, wherein the soft precursor consists of a soft deformable portion and a soft peripheral portion surrounded, the soft deformable portion is made of magnetic particles and polymer, and the soft peripheral portion is made of a magnetic particle, a mixture of organic liquid, and polymer; and extracting the organic liquid by an organic solvent shrinks the soft peripheral portion, buckles the soft deformable portion towards one side.