Abstract: Base on eigenvalue decomposition calculation, we discussed an automatic S phase picking algorithm suitable for local earthquake events. The algorithm needs few parameters, less computer resources and is easy to realize. By choosing seven time windows with different time length, it effectively reduce the S phase pick errors that caused by unreasonable time window selection. By taking 9 855 three-component records of Fujian seismic monitoring network, we test the applicability and accuracy of this algorithm. The results show that average S phase picking error by this method is （0.003±1.34） s, 79.6% of them are within 0.5 s, 4.1% of them are greater than 2.0 s, which indicates that the algorithm can meet the demands for daily S phase picking. All above-mentioned suggests that the quality of records is the most important factor that affects the accuracy of picking results, the S phase picking errors for high signal-noise ratio records are usually smaller than those for low signal-noise ratio records, and the accuracy of S phase picking for some low signal-noise ratio records will be improved after a band-pass filter preprocess.