Abstract: Aiming at the real-time in-situ detection of the thickness of cobalt-rich crusts in manned submersibles, an ultrasonic thickness measurement system of cobalt-rich crusts was designed. The physical characteristics of cobalt-rich crusts and the principle of thickness measurement were analyzed, and the hardware scheme based on ARM chip thickness measurement was designed. Based on the processing of the sampled signals of cobalt-rich crusts, the scheme proposes a peak detection algorithm for cobalt-rich crusts. Finally, a simulation test device was set up in the laboratory to test the sample. Experiments show that the peak detection algorithm can effectively identify the top echo and bottom echo time of the cobalt-rich crust samples, the thickness of the measured crust can be calculated, and the accuracy is high.