Abstract: An important task of fishing gear designers is to develop effective selective fishing gears by optimizing its geometry. The high accuracy hydroacoustic system for codend geometry measurements was designed for developing the construction of cod codend for the Baltic fishery. The system consists of 10 pairs of hydrophones, measuring microprocessor device and notebook computer. The high frequency short pulse excitation combined with the matched digital filtering make it possible to obtain high resolution of measure data. Additionally the thermistors mounted in the hydrophones are used to calculate the local sound velocity and enable precision calibration of obtained measuring data. The construction solutions, the measuring procedure and examples of obtained data are presented below.