This paper studied chaos synchronization via unidirectional coupling. The self-synchronization of Lorenz system, modified coupled dynamos system and hyperchaotic Chen system was studied by three methods: the Lyapunov stability method, the global synchronization method, and the numerical calculation of the largest Lyapunov exponent method. In regard to application to communication, we show that, by transmitting single signal, one can achieve synchronization of the drive system and the response system. An example of applying self-synchronization of hyperchaotic Chen systems to chaotic masking secure communication was addressed. Simulation results show the effectiveness of the method.