Abstract: Laser induced fluorescence (LIF) technique was applied to investigate the temperature distribution in rod bundles with spacer grid. A visual experiment facility was designed using matching index of refraction (MIR) approach. The point-to-point calibration relations of temperature and light intensity applied to rod bundle were presented. Accordingly, temperature field was reconstructed with the calibration relations. The results show that temperature field of downstream of spacer grid can be obtained using LIF technique. The influences of different heating forms, flow rate and heat flux on temperature distribution were analyzed. Meanwhile, temperature difference on the same axial height and temperature non-uniformity were adopted to evaluate the mixing performance in rod bundle. The mixing performance increases gradually on 0-4D_h downstream of spacer grid, and then decreases with the height. It is concluded that LIF technique is applicable to non-intrusive and full-field measurement in rod bundles, and it can be used as good provider for data base to validate CFD codes and evaluate the spacer grid performance.