Hovering autonomous underwater vehicle (HAUV) play an important role in short distance underwater inspection mission. There are a lot of disturbances and uncertainties underwater, a robust control is needed to minimize the effects of external influences on HAUV's system behaviour, subjects to the constraint of not having a complete representation of the HAUV system. This paper describes the development of robust sliding mode depth control of a thruster propelled HAUV. Simulation results are presented to illustrate the performance of designed sliding mode depth control.