Based on the interaction mode on customer side， the generation and load integrated static security checking mode and model are developed. In this mode， both the generation and demand side interactive resources can be optimized at the same time to improve the security performance of system after N -1 contingency in the stressed cases. In response to computational difficulties brought by N -1 contingency constraints and interaction loads in large scale systems， a decomposition algorithm with identification method of active interaction integer variables is proposed， and the optimization space as well as the computation complexity of the mix-integer program problem can be effectively reduced by using this algorithm. The effectiveness of the model and algorithm proposed are demonstrated by numerical experiments on a New England 39-bus system.