Cold seepage, stemmed from the decomposition of natural gas hydrate below the seafloor and controlled by the seawater pressure gradient, is mainly composed of water, hydrocarbons, hydrogen sulfide or carbon dioxide, and its temperature is similar to sea water.As an important prospecting area for hydrate resource in South China Sea, aplurality of cold seepage areas have been found in recent years, but it seems still unclear such as the exact time, dimensions, trigger mechanism of gas hydrates decomposition, and its relevance to climate change and sea level change in most parts of the South China Sea.In order to quantitatively study the effect of sea-level falling on the formation of cold seepage, the dynamic finite element model of hydrate decomposition was established based on the analysis of the characteristic of cold seepage to simulate the seepage Darcy velocity on different permeability conditions and the changes of excess pore pressure caused by hydrate decomposition with time.Firstly, calculate uplifting height of the base of gas hydrate stability zone (BGHS) based on the falling height of sea level, the natural gas hydrate phase equilibrium equation, the hydrostatic pressure formula, the temperature-depth equation of seafloor and the temperature-depth equation of deposition layer.Then establish two-dimensional axisymmetric model according to the characteristic of cold seepage, and set its material properties according to the previous studies on the composition of seafloor sediments and the properties of methane hydrate, methane, and sea water.The timeframe for this study is set as 26500years, starting from the beginning of the Last Glacial Maximum (26.5ka BP), and the hydrate decomposition time is set as 7500years.The computational time step is set as 100years.The excess pore pressure of upper boundary and lower boundary is set as zero, the right boundary set as impervious, and the left boundary is set as symmetric.Use structured quadrilateral mesh generation method to divide the model, and refine the mesh of hydrate zone and tubular channel.Finally, solve the two-dimensional axisymmetric unsteady seepage flow equation by the finite element method, and quantitatively analyze the influence of the sea-level falling on the formation of cold seepage.The main results are as following: (1) With hydrate decomposition lasting, the maximum value of excess pore pressure gradually increases, the area moves up, the range of fluid diffusion enlarges, and the highest excess pore pressure in the decomposition zone can even rise to 13180 Pa.But at the same depth, the excess pore pressure of tubular channel is larger than that of the sediment above the decomposition zone, and the range of fluid diffusion around tubular channel changes with depth.After the hydrate decomposition stops, the maximum value of excess pore pressure is smaller and smaller, but the range of fluid diffusion is larger and larger.Finally a funnel is formed at the bottom of the tubular channels, and the range of the funnel increases with time.