At present time, only necessary conditions of chaotic synchronization are known, and applications of chaotic synchronization is limited. In this paper, sufficient conditions of continuous chaotic system synchronization and the proofs are presented, and evolutive range of state variables is presented, too. We proved the conditions are realizable. As an application of the theory, we proved sufficient conditions of time-varying parameter chaotic synchronization, and made simulations by Chua circuits. Time varying parameter chaotic synchronization communication has high security performance, and the simulations that it defeat all kinds of attacks of eavesdroppers are presented.