We describe the problem of chaos synchronization with rigorous mathematical theory, and convert it to the analysis of stability of the differential equations. Chen's system, which belongs to the Lorenz's group, has been introduced as a typical system for discussing the stability of the linear coupled chaotic systems. A theorem on the sufficient conditions for attaining the chaotic synchronization has been proposed and a detailed proot is given. Using the conditions discussed above, a method of identifying the coupled parameter is also developed. Eventually, the results of simulation prove the validity of the theorem, and demonstrate the synchronization phenomenon of coupled systems in different ways and for different systems.