Abstract: Underwater acoustic transponder usually plays an indispensable role in underwater measurement, positioning and navigation. For the demand of a long-term real-time control underwater acoustic transponder, a set of transmitting and control circuits is designed. The transmitting circuit uses the D-class power amplifier as a main circuit and combines the impedance characteristic of transducer and tuning matching method to achieve high efficient broadband matching, and the working state of the transmitting circuit is monitored by single-chip microcomputer and I²C-to-USB converter. In this way, the transponder can select the stored signal waveform according to the remote control instruction and parameters to respond, and can also calculate the signal waveform in real-time. This transponder is very flexible and easy to control the acoustic source level. The results of lake and sea trials show that the transmitting and control circuits of the transponder are stable and reliable, can meet the needs of long-term engineering application.