The buoyancy adjustment capability is crucial for underwater robots. Dielectric elastomer (DE) is promising to be designed as inflatable actuators to achieve quiet, fast, and effective buoyancy adjustment. However, the buoyancy adjustment of DE actuators is limited by voltage amplification and controllability. This paper presents to solve the limitation of the DE buoyancy adjustment actuator by magnetic enhancement. An actuator is designed with a two-stage buoyancy adjustment capability. The two-stage adjustment strategy allows the actuator to achieve higher buoyancy adjustment at low voltage and controllable buoyancy adjustment at high voltage, where the switch between the two stages is achieved by tuning the snap of the magnet. A theoretical model is developed to assess the performance of the actuator in the two stages and describe the snap behavior. The experiment results agree with the simulation, and the actuator demonstrates the ability to adjust attitude by changing buoyancy at high voltages and rapidly ascending at low voltages. The multiple buoyancy adjustment capabilities of this actuator have the potential to enable the underwater robot to fulfill various complex task demands.