Abstract: Gas hydrate is an important potential energy source for the 21st century. The mechanism of seabed environmental variation and the environmental effect of pilot production must be studied before the exploration and production of gas hydrate to be carried out. In this paper, a seabed in-situ monitoring system is introduced for collecting serial long-term environmental data in the areas where gas hydrate occur. The design principle, constitution and integration of the in-situ monitoring system are explained in details. The system has the capability to provide long-time serial data service as a good solution for monitoring the changes in seabed environment.