Low frequency oscillation is one of the key factors threatening the security and stability of interconnected power grid. Negative damping mechanism low frequency oscillation and forced power oscillation ever have occurred in China. Based on the combined real-time multi-information sources multi-information source of WAMS and EMS, a comprehensive prevention and control method including real-time monitoring and early warning of low frequency oscillations, disturbance source localization, online searching of dynamic stability control strategy applied to large grid is proposed. The overall system function architecture is elaborated and the parallel prevention technical solution of multi-mechanism low frequency oscillation is introduced. By Prony calculation, oscillation energy index, eigenvalue sensitivity analysis of operating parameters and pattern matching strategy methods, the online warning and prevention of low frequency oscillation is achieved, the key technologies involved are pointed out. Using the proposed system, the fast quantitative evaluation and decision support for low frequency oscillation of large power grid can be implemented, and the dynamic security early warning and preventive control level of power grids can be enhanced, which is meaningful both in theoretical guidance and engineering practice. The method gets practical application in Henan interconnected power grid.