Dissolved methane in sea water not only has a great impact on global warming and the marine environment, but also it is one of the useful methodologies to recognize gas hydrate deposit. It is required to develop novel in situ monitoring technology to observe and to understand the process of methane flux. The advantage of in situ sensors is that it can be deployed underwater to obtain high spatial and temporal resolution information in real time, and  that  it makes great contribution in  the research of marine environment and global climate, as well as in finding marine gas hydrate. This paper overviews  the principles  and characteristics of in situ methane sensors for marine application and the prospects of the in-situ methane sensor  are  discussed. It is indicated that the development of new membrane materials and the detection method by combination of optical detection technology with plasma resonance and surface-enhanced Raman scattering method could play an important role for the new generation of the in-situ methane sensor in the future. 