Abstract: To solve the problem of inaccurate estimation of propagation method (PM) under low signal-to-noise ratio (SNR) and small snapshots, which exists in the process of two-dimensional L-shaped array parameter estimation, an improved PM in two-dimentional direction of arrival (DOA) estimation algorithm based on array expansion was proposed in this paper. In this method, the covariance matrix was extended and rearranged by using the rotation invariance characteristics and the propagator was got through the covariance matrix.Then the relationship was obtained between the block propagation operator and the array flow pattern by using the extending covariance matrix, which further improves the estimation performance. Then the elevation angle was matched with the azimuth angle through fast pairing method, in turn, an accurate estimation of the angle was achieved. Compared with the existing algorithms, the proposed method is more suitable, accurate and practicable, especially in the case of low SNR and small snapshots.Simulation experiments show that the proposed algorithm has better two-dimentional DOA estimation performance.