Abstract:The basic theoretical background,control equations and computation principle for solving thermo-hydro-mechanical(T-H-M) coupling problem in UDEC(Version 4.0) of 2D discrete element method are presented. Against the coupled T-H-M processes(here “H”is non-wetting fluid) in near field of drift scale test for geological disposal of high-level radioactive nuclear waste at Yucca Mountain,Nevada,USA,a numerical simulation is carried out by using UDEC. The changes of displacements,principal stresses,joint apertures,non-wetting fluid pressures and flow rates are analyzed. Some calculation results are compared with in-situ measured data and other results obtained by finite element and/or finite difference methods. The following results can be obtained. (1) The distributions and changes of temperatures and stresses are close to each other for the three results. (2) The displacement distributions obtained by UDEC approach qualitatively those of LBNL analysis;and both of them have obvious quantitative differences when heating time is shorter,but the differences are within the same magnitude order. (3) When the heating time is longer,the approaching extents of the measured data of the displacements by UDEC and those by LBNL analysis are match on the whole. So it can be considered that the simulation of coupled T-H-M processes in geological disposal of nuclear waste by discrete element method is practicable.