In this paper, the important methods is studied including frequency stability, short circuit ratio, primary frequency control ability, frequency regulation principle. The concept of “stability and control measure” is put forward and defined. The islanded operation and its influence on the northeast grid will be investigated which involves the maximal transfer power of the YiFeng AC lines and the verification of stability and control measures. The coordinating strategy between the spinning reserve and the frequency controller is proposed by studying the spinning reserve and its release, frequency controller, general frequency regulating ability. By studying the breaker, the disconnection boundary and the disconnection strategy, the operation mode can be determined. The critical flow through the breaker is put forward and defined. The islanded operation mode and stability and control strategy are studied. The fault cut time, the velocity of increasing/decreasing the DC power and the regulating step have an important influence on the islanded frequency stability. By studying integrating the islanded system into the HEILONGJIANG power grid, the connection strategy is decided. At last, the connection strategy of the local grid is determined and the overvoltage is studied in the Hulunbuir island .