The traditional tie-line generation schedule is entirely based on the electricity transaction, hence it is independent from the generation schedule of local unit, and is not influenced by the load. These cause difficulties in resource allocation and safety and stability of power grid’s operation. Thus, according to the influence characteristic of tie-line on power grid, this paper divides the execution scenes of power grid into three ones, i.e. difficult peak shaving, high capacity of running thermal power and stable load respectively, builds three optimal dispatch modes for those scenes, whose objective functions are the maximization of grid safety margin, target tie line’s absorption capacity and local wind power’s absorption capacity. Meanwhile, the warning strategy model which aims at the possible safety problem during tie line connecting to the grid, including the lack of adjust capacity of thermal units, differences in change trend of tie line and load, is proposed. Finally, a case study based on practical data of a certain power grid is given to show that the models and the methods in this paper are of validity and applicability. This work is supported by National Natural Science Foundation of China (No. 71401055).