According to the National Data Bouy Center(NDBC), the standard wave measurement system is not real-time processing[1]. But the wave measurement system in real-time becomes essential. Because postprocessing system is impossible to get wave height and its rate of change immediately. Therefore, this paper focuses on the problems of wave height measurement using the inertial sensors and then describes the development of the wave height measurement system in real-time without any other sensors. The developed system is expected to get height and relative height data of ship and buoy in real-time.