The authors use a ultrasonic transducer emit ultrasonic to simulated seabed tiny terrain,then analyze and calculate the relativity of amplitude according to the time,phase and amplitude etc included in echo signal and making using of the relativity of amplitude characteristics,at last gain the real-time altitude data of tiny terrain for deep-sea cobalt crusts mining in order to provide the parameter of best cutting depth for the intellectualized mining of excavating head.The results of theoretic analysis and indoor primary proving test indicate that this method is practical and feasible.