A three-dimensional coupled model of heat transfer tube and trefoil tube support plate (TSP) is developed based on a full-size steam generator (SG). The CFX thermal phase change model is adopted to numerically investigate the flow and heat transfer behaviors of the secondary side fluid. And the effects of trefoil TSPs and inlet subcooling on the thermal-hydraulic characteristics of tube bundle are obtained. The calculation model reasonably reveals the distributions of the flow and heat transfer parameters in the SG, especially in trefoil TSP regions. Based on the across flow velocity and density of the secondary side fluid in U-bend region, the most severe flow-induced vibration damage is predicted at the angles of 110 degrees on the hot leg and 60 degrees on the cold leg, respectively. Due to the effects of trefoil TSPs, vortexes are induced, the outer wall temperature in the circumferential direction shows periodic characteristic in TSP regions, which increases the possibility of aggressive solutes deposition and U-tubes rupture. In addition, inlet subcooling of the secondary side fluid has significant effects on the SG. As inlet subcooling decreases, the heat transfer is enhanced. The numerical simulation results obtained may provide guidance to facilitate the optimal design and in-depth thermal-hydraulic analysis of TSPs and SGs.