Quick and accurate extraction of the power-frequency phasor from transient fault signals is crucial for relay protection.Using the sum of damping exponents to approximate the original signal，the least-square matrix pencil algorithm can avoid the impact of decaying DC components and fractional harmonics.This paper studies the influence of the sample frequency，the length of data window and model order on the least-square matrix pencil algorithm and analyzes the influence of filters and data sampling on the algorithm.Finally，compared with the Fourier algorithm in one cycle，the least-square matrix pencil algorithm is found to be more accurate.