In this paper, three-dimensional numerical simulations were conducted to study the thermal mixing of turbulent flow in a T-junction pipe where hot fluid was flowing in the main pipe and cold fluid was in the branch. The main objective of this research is to investigate the effects of the angle between axial and cross injection flows and the branch to main flow rate ratio on the turbulent thermal mixing. In this regard, an appropriate mixing index was proposed to evaluate the thermal mixing efficiency. The turbulence model employed in this research is the SST k-? model that can properly capture the mixing behavior of the flow in the main pipe. The results show that the cross injection angle can considerably affect the thermal mixing enhancement. However, the effects of injection angles on the thermal mixing at lower flow rate ratios are more significant.