For the detection of underwater trashes, the ultrasonic detection system is a necessary deceive. In the traditional ultrasonic detection system, echo signal is generally processed by analog circuit, and only the distance information is obtained. In order to determine the distance and material of target, the amplitude of echo wave also need to be extracted, and FPGA is employed to control high-speed AD and process data. The design of control circuit based on FPGA is presented here. The control circuit includes modules of clock, high-speed data processing, communication and transmitting control. On the basis of the system design, simulation, implementation, the system experiments are completed. The results show: the functions of the control circuit based on FPGA are implemented correctly, but the system power consumption needs to be reduced more.