Firstly, the Iridium system and SBD (Short Burst Data) service is introduced. Secondly, the marine environment monitoring system is designed based on Iridium SBD. Finally, the realization of the Iridium SBD transmission subsystem is provided. The main function of the system is to obtain the collected data by the underwater sensor. The information will be uploaded to local control center by iridium communication after fixed time. At the same time the sensor should receive commands from local control center by iridium communication.