Abstract: The inherent time delays in the control loops of power systems will affect the performances of controllers and even endanger the stable operation of the system. Therefore, an eigenvalue calculation method based on the partial infinitesimal generator discretization with implicit Runge-Kutta（PIGD-IRK）is proposed for analyzing the effect of time delays on small disturbance stability of large-scale power systems. Firstly, the bottlenecks that restrict the computational efficiency of infinitesimal generator discretization with implicit Runge-Kutta（IGD-IRK）are analyzed. Secondly, by applying the partial spectral discretization idea, the dimension of the infinitesimal generator discretization matrix constructed by IGD-IRK is greatly reduced. Thirdly, the echelon block discretization matrix is further transformed into the product of the inverse of a constant matrix and an upper triangular block matrix by taking advantage of its structural characteristics, thus the sparsity of the discretization matrix and system augmented state matrix can be fully used in the process of eigenvalue calculation. Finally, the accuracy and high efficiency of the proposed method are verified on a two-area four-machine system and two actual power systems.