A flexible underwater robot, a control method and a device is provided with at least one movable joint and a control module. A flexible joint module of the movable joint comprises a first connecting plate, a second connecting plate, a first spring, several second springs, several third springs, several first pulling ropes, several second pulling ropes and a pulling module. The first spring, the second springs and the third springs are arranged from inside to outside in sequence with gradually decreased rigidities correspondingly to form a gradual rigidity structure, so that it is more flexible to adjust a posture. When the robot is impacted, it may absorb and release energy to ensure the integrity of the flexible joint module, so that the stability is improved.