HY-2A is the first satellite for oceanic dynamic environment measurement of China. As one of main payloads of HY-2A, HY-2A radar altimeter has obtained successive measurement data after the launch. The accuracy of HY-2A radar altimeter is better than 4 cm (at 20 m significant wave height) or 2 cm (at 4 m significant wave height), which is close to that of Jason-2 satellite altimeter. In this paper, the design and in flight preliminary results of HY-2A radar altimeter are introduced.