Considering the differences between the source-grid-load coordination in different operation modes of power grids, a source-grid-load coordination identification and control method are proposed in this paper based on trend theory. Firstly, the directional derivative is used to investigate the relationship between the overall power angle safety index and the load balance degree of the grid. According to the difference analysis between the equilibrium of power grid operation and the load balance degree of path, the imbalance between source-grid-load can be identified. Then, based on mapping elasticity potential energy model of power grids, the physical analysis of local grid can be performed. It is found that the minimum singular values of the Jacobian matrix and the output or load of power generation have the same trend. Finally, a source-grid-load coordination identification and control method are proposed. The IEEE 9-bus system is selected to verify the theorical result that the overall power angle security index and the path load balance have the same trend and has no relationship with the balance of power grid operation. The IEEE 39-bus system is used to verify the effectiveness of the source-grid-load coordination control method.