This paper presents an optimal model for AGC using OPF technology for interconnected grid. Based on traditional OPF model, the model takes into account security constraints, generator and load static frequency regulation characteristics. Generator unit ramp rate constraint, frequency constraint and transmission interface power constraints are added. Meanwhile the auxiliary adjustment expense of AGC units is used as objective function. The new model expands the application range of OPF model, makes it extended to the real-time electricity decision method from power generation plan control decision method, and avoids the regional deviation result from traditional AGC strategy and the risk of security constraints limit. The new model is tested on modified IEEE-39 bus distribution system and solved by predictor-corrector primal-dual interior point method, correctness and validity of the new model are validated.