Recognizing the faultiness of ignoring that thermophysical properties of transmission medium varied with the temperature, a comparative assessment of two cases was performed by computational fluid dynamics (CFD) method in capturing braking performance, internal flow field and fluid structure interaction for hydraulic retarder. The case considering the variation of thermophysical properties greatly improved the prediction accuracy due to the simulation conditions closer to experiment. Braking torque could be increased because of the enlargement of density and the reduction of viscosity, while there was no obvious effect on braking performance for specific heat and thermal conductivity. For internal flow field, the enlargement of density and the reduction of viscosity together lead to an increase in velocity, which in turn resulted in an increase in pressure, then the reduction of viscosity could suppress the generation of vortices reflected by the decrease in vorticity, which could positively reduce the energy loss near the wall. Finally, a comparative analysis between fluid structure interaction (FSI) and thermal fluid structure interaction (TFSI) was conducted. The results indicated that the deformation and equivalent stress significantly increased compared with original simulation conditions due to the presence of thermal stress, which obviously increased the stress damage of hydraulic retarder housing. (C) 2017 Elsevier Ltd. All rights reserved.