With the developing of power system, there many power plant of HUBEI JINGZHOU CHINA with small generation capacity interconnected with weak lines and more and more small capacity interconnected to power grid threaten the stability of power system. The small capacity system is not normally meet local load (contrariwise), and sometimes even larger shortage. Aimed at the different types of small electric power grid when interconnected-line fault. There is practical and difficult problem that how to ensure that the small power grid can be quickly restored stability when separated for system. Simulation shows the contribute and motion-time confine of generator.