Abstract: Due to its lower vertical resolution (about tens of centimeters), the conventional geo-sonar equipment is unable to be used for detecting the thickness of submarine cobalt-rich crusts (about 1~25 cm) accurately, therefore a parametric array sonar system is designed. In this system, the multi-pulse superposition technique is used to suppress noise and improve signal-to-noise ratio, and the dual-frequency time-delay estimation technique is used to improve the detection accuracy of crust thickness. The detection principle of the system is as follows:the primary frequency echo determines the echo arrival time from the water-crust interface, the peak of the difference frequency echo envelope is detected for estimating the echo arrival time from the crust-bedrock interface, and the thickness of the crust is calculated by the time delay difference of the echoes from the upper and lower interfaces of the crust. The system was used to measure the cobalt-rich crust with a thickness of 15 cm and the measurement results consistent with those of core sampling. The system proposed in this paper has certain reference significance for the development of subsequent relevant detection equipment.