In this paper,first,the sliding mesh technology and the computational fluid dynamics （ CFD） technology are both applied to solve the Navier-Stokes equations of a ducted propeller which governs the fluid motion around the duct. Then,the thrust characteristics of the ducted propeller in the flow field of an underwater robot in turning motion are simulated,and the hydrodynamic phenomenon of the propeller in such a condition is observed. The results indicate that,when the flow comes from the robot stern,the thrust coefficient of the stern propeller is lower while that of the side propeller is higher than that without robot,that the flow from the robot frontage may result in an opposite case,and that the robot has no obvious effect on the thrust coefficient when the direction of incoming flow is approximately perpendicular to the axis of the robot.