<p>Recently, variable geometry turbochargers (VGT) that effectively recycle exhaust gas energy have been actively introduced to improve the performance of gasoline engines. In particular, in order to effectively drive VGT under low exhaust energy conditions, variable vanes must be used to implement optimal flow conditions for the turbine impeller of the VGT according to the operating conditions. In particular, for VGT that operate at lower pressure ratios and higher exhaust gas temperatures than diesel engines, accurate evaluation of turbine performance is a very important indicator during the development process. In this study, a conjugate heat transfer analysis (CHT) model was constructed using a VGT consisting of 93 parts. In addition, high-pressure and high-temperature exhaust gas on the turbine side to drive the VGT, atmospheric air on the compressor side, and oil and cooling water to drive the bearings that support the turbine and compressor impeller were added to the VGT model. Using this finely constructed model, a study was conducted to identify the effect of selecting convective heat transfer coefficients on evaluating turbine performance in the process of performing complex flow and heat transfer analyses. Through this study, we were able to confirm that the selection of the correct heat transfer coefficient is very important in evaluating the temperature distribution of the components constituting the VGT, but does not have a significant effect on the evaluation of the VGT efficiency.</p>