Since the special structure of U-tube steam generator, so the secondary side fluid will receive non-uniform heating from the primary side. When U-tube steam generator is applied in ocean environments, it may be in an inclined condition, and the inclined condition will make the thermal-hydraulic characteristics in the secondary side of U-tube steam generator more complicated. In this paper, a series of experiments under different inclined angles were conducted to investigate the effect of inclination on the heat transfer characteristics in tube bundle channel. Besides, the coupling effect of non-uniform heating and inclination is considered. The results show that the inclined condition will lead to an angle between the hot-cold fluid interface and the fluid temperature measuring interface, and it can also generate a gravity component perpendicular to the flow direction, which can drive the fluid to flow laterally through the tube bundle. Both of them lead to the radial inhomogeneity of fluid temperature under uniform heating condition. Furthermore, non-uniform heating can also cause a radial unevenness of fluid temperature at the same level, and the trend of unevenness is determined by the heating power and the heating power ratio. The final results are shown in a coupling superposition effect of inclination and non-uniform heating, and it can be an enhancement effect or a weakening effect according to the direction of inclination.