Abstract: With respect to the precise three-dimensional trajectory tracking problem of an underwater vehicle, a finite-time disturbance observer-based continuous control strategy is proposed in the presence of both external disturbances and unmodeled dynamics. Firstly, the finite-time disturbance observer is devised to quickly observe lumped disturbances of the system, and thus the anti-disturbance ability is dramatically improved. Then, by combining with nonlinear feedback and accurate feedforward signals, a continuous three-dimensional trajectory tracking controller is synthesized under the framework of backstepping control, so as to facilitate executions by actual actuators. Also, the closed-loop system is strictly proven to be finite-time stable in the Lyapunov sense. Finally, three-dimensional trajectory tracking simulations are conducted on the famous "REMUS" underwater vehicle. Simulation results show that the proposed control strategy can accurately compensate lumped disturbances of the system, and thereby the underwater vehicle can briskly and precisely track the three-dimensional reference trajectory.