Abstract: <abstract>    A model consisting of 12-node infinite domain elements and 10-node infinitedomain elements and the complete set of formulaeare presented In this paper for three-dimensional problemes。 On the basis of the calculation examples the problemsassociated with the application of elements of this sort are discussed, Such as the decayfunction and the decay center and so on。    The introduction of these special elements into the infinite or semi-infinite domainFE analysis of the geomechanlcal engineering problems leads to a satisfactory calcu-lation accuracy and the fulfilment of the boundary conditions of zero displacement atinfinity, with only a limited or even a small calculation region being taken intoconsideration, Thus it comes as an effective approach to determination of the calcu-lation region and boundary conditions, and has the apparent advantage in the calcu-lation accuracy, economy and effectiveness.