The invention relates to the safe and stable operation of an electric power system and discloses a method for preventing and controlling the low frequency oscillation of a power system with synergy between a power source and a power grid. According to the method, the influences of power source side unit control system parameters and power grid side structure and operation mode changes on the dynamic stability of the power system are considered comprehensively, and the dynamic stability level of the power system is improved through a mode of the synergy between the power source and the power grid. When a power grid structure or an operation mode changes, the unit control system parameters are reset through a genetic optimization algorithm, and low frequency power oscillation caused by no synergy between the power source and the power grid can be effectively prevented.