The depth hovering control problem of robots is studied such that the designed oil-immersed transformer inner detect robot can observe a specific depth direction point during the practical operation. By analyzing the control strategy of robots, according to the underwater robot dynamic theory, the dynamic model of robots in the transformer oil special medium is established. A robust backstepping sliding mode control method is proposed based on the robust backstepping control method and the adaptive sliding mode control theory. Meanwhile, a fuzzy controller is used to design the sliding mode surface switching gain to reduce the chattering caused by uncertain disturbances, and the stability of the control system is analyzed based on Lyapunov theory. Consequently, the spin and chattering problem of robots caused by coupling and external disturbance during the depth hover in transformer oil is solved. Finally, simulation and experiment results show the effectiveness of the proposed controller.