Abstract: This paper proposes a double closed-loop Terminal sliding mode control methodology with model parameters uncertainty for the trajectory tracking of fully actuated unmanned underwater vehicles under external current disturbances. Firstly, to prevent the problem of large overshoot during the position and orientation control of UUV, the position and orientation negative feedback is introduced, and the reference velocities are defined in the outer loop, which serves as the virtual control law in stabilizing the tracking errors of position and orientation. With respect to the inner loop, the virtual control law is taken as the tracked target. Considering the undesirable chattering effects of conventional sliding mode control methods, a non-singular Terminal sliding mode controller is adopted, which eliminates the chattering effects as well as ensures the velocities' tracking error on the sliding surface to converge to a steady state within finite time. Finally, the stability of the proposed system is analytically proven using the Lyapunov stability theory, and the simulation results show that the control scheme guarantees precise spatial trajectory tracking of UUV.