Abstract: Security constrained economic dispatch（ SCED） for large-scale power grid is an effective technical way to solve the problem of large-scale optimal allocation of resources. Different from optimization scheduling of single provincial power grid,on the one hand the calculation scale of SCED in the large-scale power grid increases greatly,and on the other hand it is necessary to coordinate the unit and tie-line transmission plan reasonably on the premise of considering the actual business and characteristics of national（ regional）and provincial dispatch. It is more difficult to construct and solve the model because of the expansion of computing scale and more complex constraints. This paper focuses on the model description of balance strategy,tie-line planning and large-scale network constraints,and constructs a SCED model for different needs by optimizing the selection of objectives and the configuration of constraints,so as to achieve a reasonable match between solution performance and usage effect. The effectiveness of the proposed method is verified by simulation of a real power grid in China.