The more and more operators and researchers of power grid have realized that the synthetic defending measures are important to avoid large scale blackout. The existing forewarning and preventive control systems focus on the real-time and on-line security and stability analysis and defending measures, but considering the whole process of power grid operating and production can realize a systematic and synthetic defending. The system engineering idea is applied to four important steps in power grid operating and production, and security and stability analysis and preventive control measures should be adopted. And so, four-grade forewarning and preventive control method is presented. The implementation of four-grade forewarning and preventive control method for secure and reliable operation of Henan power grid is introduced. The main content is implementation of detailed functions, innovative technology applications, and thinking and inspirations of application. It provides reference for future development of early-warning and preventive control system.