In this thesis a parallel simulation platform, namely TOUGH2MP-FLAC3Dplus, was further developed by linking the multiphase multicomponent flow code TOUGH2MP and the further developed geomechanical code FLAC3Dplus for large-scale simulation of the coupled THM/C processes related to geo-energy production. A series of mathematical/physical models were developed and implemented in this platform, including (1) an improved equation of state for CO2-CH4-H2O-NaCl system which considers the effect of salt on phase partition and fluid properties in gas reservoirs; (2) a modified coupling approach for the simulation of hydraulic fracturing in tight geo-reservoirs, which considers the multiphase multicomponent leakoff effects; (3) a thermo-hydro-mechanical model based on a crack tensor for naturally fractured rock masses and faults. All these verified models have been applied in three different case studies, including CO2 enhanced gas recovery (EGR) in the Altmark natural gas field; (2) Hydraulic fracturing in three different types of geo-reservoirs (tight gas, oil and geothermal reservoir); (3) Geothermal energy utilization induced seismicity in Unterhaching. The developed models and the numerical platform can be used to predict the coupled THM/C behavior of rock formations, to optimize the CO2-EGR and hydraulic fracturing in tight geo-reservoirs, as well as reduce the geo-risks related to geo-energy production.