To enhance the detection accuracy of underwater platforms for targets, this paper designs and validates a sonar system mounted on the flank side. The system omprises a hytrophone array and an electronic subsystem, operating in passive sonar mode. System employs phase-shifted beamforming technology to process received signals in the spatial domain for target azimuth estimation, and utilizes matched filter technology to process echo signals for target range estimation. The electronic subsystem incorporates low-noise signal conditioning and synchronous acquisition modules to achieve low-noise synchronous capture of 48-channel acoustic signals, and features a high-speed, large-capacity storage system to ensure real-time data recording. Experimental results demonstrate that the electronic system self-noise spectral density is as low as 2.52 nV/√Hz @40 kHz, with inter-channel amplitude consistency error below 0.4 dB and phase consistency error under 2°. The system exhibits an overall amplitude consistency error of better than 3 dB and a phase consistency error of below 6°. It is capable of achieving a resolution of 2.10° and 1.35 meters, with a localization error of 3.96° and 2.12%.