This paper studies synchronized motion of the master-slave autonomous underwater vehicles under the constraints that the capacity of communication channel is limited. The dynamical models of both the master vehicle and slave vehicle are mathematically given in form of fully-actuated Euler-Lagrange equation, and a master-slave motional-state synchronization scheme coupled by a saturated state-error feedback controller is established under the consideration of binary coding-decoding procedure. A definition of robust synchronization with error bound is introduced, then, by means of Lyapunov stability theory, some synchronization criterions are derived and the corresponding synchronization error bound is estimated. Both of the theoretical analyses and the final numerical simulation show that the synchronization error bound is inversely proportional to the channel capacity.