Under water shaking table experiment was carried out to strudy the vibration characteristics of the soft landing structure, which is landing on the under sea soft grand. After consolidation of the clay layer on the shaking table, the models of soft landing structure were set on the underwater clay layer with buoyancy pressure, and shaking test was carried out.
　The results of experiment shows following. At the lower input acceleration level, the response acceleration of soft landing structure is larger than input level. But at the higher input level, the peak of the response was appeared at the head of wave, and after the peak, the response was decreased and stabled to lower level. The maximum horizontal force (Smax) from claylayer to model at the peak acceleration was obtained from the equation : Smax=0.21c・A (c:shear strength of clay, A:area of base). The behaviour of soft landing structure during the earthquake could be simulated by the simple calculation method of non-liner one-mass model.