The invention relates to the technical field of electric power system transient stability analysis, and discloses a voltage online coordination control method based on energy margin constraint. The voltage online coordination control method based on energy margin constraint comprises the following steps that (2) a system potential energy function model Ep is built, and an energy margin Em is calculated on the basis of the lie derivative; (2) an approximate linear programming problem is formed by using the energy margin Em as an objective function and using the reactive margin and the voltage allowable change range as constraint conditions; (3) a coordination control strategy is obtained to accomplish coordination of various voltage control modes. According to the voltage online coordination control method based on energy margin constraint, various voltage control modes are brought into a uniform energy function frame, the lie derivative is introduced to calculate changes of the energy margin, the approximate linear programming problem is formed by using the situation that the energy margin is larger than or equal to zero as the objective function and using the reactive margin and the voltage change range as the constraint conditions, and the solution of the approximate linear programming problem serves as the coordination control strategy. According to the voltage online coordination control method based on energy margin constraint, the calculation speed can be increased, generation of the online coordination control strategy of various voltage control modes is facilitated, and the safe operation level of a power grid is improved.