Abstract: B Patterns of after shocks burst in Jiangsu Province and its adjacent areas have been detected and its effectiveness and stability for earthquake prediction have been tested, a relatively ratisfactory result has been obtained, For 5 of the 6 strong earthquakes recently ocurred in the area, after-test prediction can be made based on B patterns, the relatalive warning time is 0.33 and the statistic mark R value is 0.50. The authors consider that B patterns may have the same physical content as the "window" effeet of stress field (regional stress field is strengthened). But B patterns can extract more precusory information from a wider space than the latter.