Abstract: The study of turbulent mixing in the tight lattice under the blockage conditions has great significance to the prediction of the thermal and hydraulic behavior of the fuel assembly under the accident condition. In the current study, numerical study on the turbulent mixing in the tight lattice was carried out. The results of simulation agree well with the literature results. The simulated velocity, vortex structure and turbulent mixing coefficient distribution of the blocked section and its downstream in different subchannel blockage conditions were compared. The variation rules of transverse and axial turbulent mixing coefficients under different blockage conditions can provide a reference for the parameter setting of the subchannel analysis program.