The one- and two-dimensional coupled map lattices in nonlinear dynamic system are used as the system model. We report a method with which the spatiotemporal chaos can be synchronized using unilateral coupling in two Bragg acousto-optic bistable spatial extended systems. The synchronization can be realized by appropriately selecting the coupling strength and the equilibrium coefficient. By calculating the largest conditional Lyapunov exponent, we obtain the minimum coupling strength for achieving the synchronization and the functional relationship between the minimum coupling strength and the system parameters. Our simulation shows that the synchronization can also be realized under the influence of small random noise, so this method is robust.