We propose a method of synchronizing chaos, which based on a certain parameter of two chaotic systems that is driven by the external chaotic signal. As a possible application we numerically investigated the synchronization of chaotic erbium-doped fiber dual-ring lasers systems. Numerical result shows that when the driving system is in chaotic state, if the driving stiffness is proper, the two chaotic systems will easily achieve completely synchronization based on new dynamics. When the driving system is in different states, the two systems can still retain synchronization, but the driving stiffness is larger than last case. On the other hand, it is found that the different synchronization states depend on the driving stiffness in erbium-doped fiber dual-ring lasers systems.