In the fuel assemblies in reactor core, the distribution of temperature is not uniform in the fuel rod along the circumferential direction. The circumferential temperature difference could be neglected for conventional assembly design but increases significantly in a tight lattice. To investigate the circumferential non-uniformity of heat transfer in rod bundles, this paper firstly establishes mathematical model and makes theoretical analyses, based on which influential non-dimensional numbers are summarized. Then, a semi-empirical correlation describing this phenomenon is proposed based on theoretical results and CFD sensitivity analyses. Finally, a three-dimensional model for cylindrical fuel is introduced in the thermal-hydraulic code to predict circumferential heat transfer non-uniformity in different geometry and flow conditions. To validate this model, some results are compared with experimental data of bundle test for subcritical and supercritical water. The three-dimensional fuel model for sub-channel code is a new numerical tool to predict the peak cladding and fuel temperature and can be applied in thermal-hydraulic analysis of fuel assemblies of tight lattice design. Copyright (c) 2017 John Wiley & Sons, Ltd.