Abstract: For improving passive ranging of three-sensor array,a sliding cross-correlator is adopted to improve the performance of time delay estimation.Compared with the traditional cross-correlator the sliding cross-correlator's ability is highly increased.An improved formula which is in high precision for near target is employed.An algorithm for kicking out wild value is presented,which is on line,can track automatically.The algorithm named "round filter" can pick out the data in high quality with robustness.A"dynamic filter"is presented,which is combined with the "round filter" as the post processor.The experimental result of three-sensor array passive ranging in shallow water and near field is introduced,which shows the post processor is indeed obvious in improving the ranging performance.