There is a large number of natural gas hydrate (NGH) resources occurred in marine sediments. The study of phase equilibrium of gas hydrate and its influencing factors is of significance to the thermodynamics and kinetics, distribution pattern and resource assessment of gas hydrate. However, the research results up to the present remain qualitative or semi-quantitative, and not much attention has been paid to the influence degree and genetic mechanisms of different factors. Recent researches suggest that there are some other ingredients which may influence the phase equilibrium of NGH in addition to temperature and pressure, such as gas composition, pore fluid salinity as well as sediment grain and pore size. In this paper,preliminary discussion was given to these factors from the view point of gas solubility, water chemistry and sediment porosity.