The invention relates to a power system security and stability control strategy determining method and device. The method includes the following steps that: the power grids of a target area are simulated through electromechanical transient simulation software, equivalence processing is carried out on original data used for electromechanical transient simulation, so that a simplified receiving end alternating-current power grid of the target area is obtained; comparative analysis is performed on the key electrical quantities of the simplified receiving end alternating-current power grid and a pre-simplification receiving end alternating-current power grid, the simplified receiving end alternating-current power grid is adjusted; electromagnetic transient models of a receiving end alternating-current power grid, a direct-current power grid and a sending end alternating-current power grid are constructed on the electromechanical transient simulation software; key electrical quantity comparative analysis is performed on the electromagnetic transient models of the power grids and a simplified electromechanical transient model, the electromagnetic transient models of the power grids are adjusted; the power grids of the target area are calculated through the electromechanical transient simulation software; and calculation results are verified through the electromagnetic transient models of the power grids of the target area, and security and stability control strategies are determined according to verification results.