The present invention relates to an electric power system excitation voltage decoupling control method based on wide-area information. The method comprises the following steps: realizing the decoupling control of the excitation voltage and frequency based on the system equivalent simplified model of the wide-area information; compensating wide-area control time delay by employing a second-order Pade approximation method, and obtaining an excitation voltage decoupling control model including the time delay compensation; and converting the excitation voltage decoupling control problem to a linear quadratic type optimal control problem, and obtaining an excitation voltage control strategy. Through adoption of the wide-area information, the present invention provides an electric power system excitation voltage decoupling control method, and therefore the decoupling control of the excitation voltage and frequency of a generator is realized, the complex non-linear excitation voltage control problem is converted to a simple linear quadratic type optimal control problem, the method of rapidly obtaining an effective excitation voltage control strategy is realized, and the electric power system excitation voltage decoupling control method has good application values and popularization prospects.