In order to clarify the mechanism of the dynamic stability of a power system following large disturbances and to look for effective stabilizing measures for the system， the correlation of low frequency oscillation， power transmission capacity and network configuration is explained through a group of curves of power-angle characteristics and the different operating points of a generator-transmission system. By comparing the difference of power-angle curves at different operating points and corresponding difference of damping effects， the dynamic characteristics of the power system following large disturbances are discussed. Based on above studies， the stabilizing measures for the system are analyzed as well. It is concluded that an effective damping effect will be provided by rapidly reducing the output of key generators following tripping of a part of transmission lines in a grid section.