Abstract: We develop a fast rupture length estimation method by using small-aperture seismic arrays beam-forming technology, and proposed a method to adjust the phase of each station. By the method the phase difference of each station can be calculated approximately, when delay of each station cannot be determined. The result of Wenchuan earthquake outline test shows that the time efficiency of this method is good, for example, at about 10 s before the arrival of peak ground acceleration, the estimation result of rupture length is about 120 km. Although this estimation has a large deviation compared with the final estimation results （about 230 km）; however, from the point of view of fast earthquake warning, it still has good practical significance. By comparing with the previous research results, it is indicated that this method underestimates the rupture length in northeast direction, and the causes and possible solutions are discussed. Finally, the computational speed of the algorithm is studied, the results show that the method can meet the requirement of real-time fault rupture length estimation by parallel computing.