The interchannel mixing effect is very important for the thermal-hydraulic performance of fuel assembly subchannels in Pressurized Water Reactor (PWR), especially for that of the fuel assembly with spacer grid. In this study, an anisotropic turbulent mixing model with a turbulent mixing coefficient matrix is developed and embedded in an in-house code to analyze the thermal-hydraulic performance of the fuel assembly. The validation of the present turbulent mixing model has been performed by comparing the numerical results with the experimental results for the outlet temperature distribution of the fuel assembly. Then, the thermal-hydraulic performance of 5 x 5 rod bundle with spacer grid is analyzed by comparing the present turbulent mixing model and the conventional isotropic turbulent mixing model which uses a constant value to consider the average mixing effect. It is found that stronger diversion crossflow, more uniform outlet temperature distribution, higher Critical Heat Flux (CHF) and higher Departure from Nuclear Boiling Ratio (DNBR) of the fuel assembly are achieved when using anisotropic turbulent mixing model. In summary, the anisotropic turbulent mixing model depicts the interchannel mixing characteristics of spacer grid more reasonably. (C) 2018 Elsevier Ltd. All rights reserved.