A thermo-hydro-mechanical coupled model was used to simulate hydraulic reaction of the PRACLAY in-situ heating experiment which was conducted in Belgium underground laboratory HADES. The 3D finite element simulation was performed for the sensitivity of parameters to the pore water pressure, effective stress and temperature of surrounding rock under thermo-hydro-mechanical coupled conditions by using a single factor analysis method. The effects of two coupling factors among temperature, seepage and stress were comprehensively investigated upon hydraulic reaction of rock around the repository. It is shown that the permeability, elastic module and thermal conductivity are the uppermost ingredients influencing the pore water pressure. The cohesion, friction angle and thermal expansion efficient have a negligible effect on the pore water pressure, but have a remarkable effect on the effective stress. The distribution of temperature field of surrounding rock is only affected by the thermal conductivity. The influence mechanism of various parameters on pore pressure, temperature, and effective stress is different. There exists a difference in the effects of two coupling factors among temperature, seepage and stress upon hydraulic reaction of surrounding rock. The strongest coupling is found from thermal to hydraulic and mechanical behaviour. The excessive pore pressure induced by heating greatly affects the stability of surrounding rock, so does the variation of effective stress caused by thermal expansion. The results of this study have a certain value for the determination of parameters and analysis of coupling mechanisms of clay tunnel for radioactive waste disposal.