In this paper, a solid model and a beam element model of an outmost U-tube of steam generator were established, and its vibration response was studied by Abaqus explicit dynamics. The vibration response of the U-tube supported by anti-vibration bars (AVBs) was studied by the solid model and the simplified form of anti-vibration bars in beam element model was studied by comparing the results of the solid model and the beam element model. The effect of gap on vibration response and fretting wear of the U-tube was studied by changing the gap between the U-tube and the anti-vibration bars. The analysis shows that: in the beam element model, the anti-vibration bars can be simplified into simple support. With the gap of the anti-vibration bars increase, the support effect of the U-tube becomes weaker, but the amplitude is not sensitive, while the wear power decreases obviously. The design of a steam generator should consider the support effectiveness and wear condition comprehensively and the support gap should be controlled within a reasonable range.