The invention discloses a numerical integration method for electric power system full dynamic simulation, combining a fixed-step trapezoidal integration method and a variable-step Gear integration method organically in the full dynamic simulation. In the method, the fixed-step trapezoidal integration method, a differential equation of a dynamic element and an algebraic equation of power network are adopted to carry out iterative solution in a mechanical and electrical transient state process of the electric power system full simulation; in the method, the variable-step Gear integration method, the differential equation of the dynamic element and the algebraic equation of the power network are adopted to carry out simultaneous solution in a medium and long-term dynamic process. The fixed-step method and the variable-step method are switched automatically according to a certain strategy in the simulation. The method integrates the advantages of the two original numerical integration methods, thereby overcoming the defect of low calculational efficiency resulting from too small step in the simulation of mechanical and electrical transient state process of the electric power system ofthe existing full dynamic simulation program while ensuring numerical calculation stability and calculation accuracy.