Abstract The simulations and numerical analyses of triaxial compression tests on soil samples recovered from the East Nankai trough have been performed by the elasto-viscoplastic constitutive equation. And the numerical analyses of the laboratory model tests on ground deformation in methane hydrate production were carried out by finite element method. From the comparison with the experimental results it is proved that the simulations can express well the behavior of experiments and the numerical analysis results can well reproduce the deformation behavior of ground in the model tests. Introduction Methane hydrate is currently being eagerly examined as a next-generation energy resource in Japan to replace oil and natural gas. The Research Consortium for Methane Hydrate Resources in Japan was established to undertake research in accordance with Japan's Methane Hydrate Exploitation Program prepared by the Ministry of Economy, Trade and Industry. To produce methane gas from methane hydrate safely and without damaging the environment, it is necessary to address many wideranging environmental issues. One of them is to assess seabed deformation during methane gas production. In the above Consortium we are investigating the deformation of seabed ground which may occur due to the production of methane gas from methane hydrate. Geotechnical properties of seabed ground have a significant effect on the deformation behavior. Soil samples were recovered from the East Nankai trough which is expected as one of the fields of natural resources of methane hydrate. We performed the soil index tests, consolidation tests and triaxial compression tests on these soil samples and estimated the geotechnical properties of soil samples based on the results of these laboratory tests. Then we identified the material parameters for the elasto-viscoplastic constitutive equation which can express the mechanical properties of the seabed ground and we performed simulations of triaxial compression tests on soil samples by this constitutive equation. Further we developed a simulator for the estimation of seabed ground deformation using the above constitutive equation. We carried out the laboratory model tests on ground deformation in methane hydrate production and we performed the numerical analyses of these model tests by this simulator. Outline of Triaxial Compression Tests The digging of wells was carried out in deep sea at the East Nankai Trough. We performed triaxial compression tests on core samples recovered from the Nankai Trough Well (Nishio et al., 2006). The triaxial compression tests were carried out in K0 consolidation undrained condition. The depth of core samples used in tests is 8.5-225.0m below the seabed surface. The samples used in the tests are mainly cohesive soil.