To investigate the underground structure of shallow water, Han-river near Yangsou-Ri, high resolution hydroacoustic measurements were carried out for the engineering design of railroad bridge. The acoustic source was a Boomer with an energy of 90 to 280J and in a frequency range up to about 16kHz. The reflected signals were received by using both traditional hydrophones(passive element) and a specially devised receiver unit(active element) mainly composed of piezofilms and preamplifier. They are connected to the "SUMMIT" data acquisition systemCDMT-GeoTec company), where the sampling interval was set to 1/32ms. The source position was continuously monitored by a precision DGPS system whose positioning accuracy was on the order of lOcm. For the quality control purposes, two different source-receiver geometries were taken. That is to say, the measurements were repeated along the profile every time depending on the different source energyC175J, 280J), the receiving elements(passive, active) and two different source-receiver geometries. It was shown that the data resolution derived from a proper arrangement with the active hydrophone could be greatly enhanced and hence the corresponding profile section caused by the regular data processing system "FOCUS" accounted excellently for the underground formation below the shallow water.