Abstract: Abstract: The open circle turbine propulsion system applied to high-speed autonomous underwater vehicle (AUV) has the outstanding characteristics of low gas consumption, large enthalpy drop and simple structure. But this system is sen-sitive to varying conditions. In this study, the closed-loop control strategy was adopted by adjusting the fuel pump angle to establish mathematical models of the open circle turbine propulsion system and the pump angle actuator. A reasonable control algorithm was designed. Based on the models and the algorithm, a closed-loop rotary velocity controller was developed. Thus, the stepless speed control of underwater turbine was achieved. Hardware-in-the-loop simulation result shows that the proposed controller can keep the system′s rotary velocity following the command velocity in varying conditions (variable depth or velocity). The transition time of the rotary velocity regulation is less than 7 s, and the maximum deviation of rotary velocity is less than 20 r/min. The combustion chamber pressure overshoot is less than 5%，which ensures the security of the system. The controller may effectively support the implementation of new guid-ance law of an AUV.