Abstract: Under ocean conditions, floating platforms and ship nuclear power plants may be in an inclined state for a longer period of time, which is one of the most basic oceanic attitudes. In marine nuclear power systems, there are lateral non-uniform heating phenomena caused by uneven local heat flux distribution between tubes and rods in core channels, U-tube steam generators, and dual process heat exchangers, leading to cross-mixing of fluids. The presence of ocean inclined conditions makes the cross-mixing characteristics more complex. When the inclination condition and non-uniform heating jointly act on the tube bundle channels, their coupled effect is also related to the inclination direction. When the position of the side with high heat flux is above or below the side with low heat flux, there will be differences in the coupled effect between inclination and non-uniform heating. The local fluid cross-mixing between tube bundles can affect the flow and heat transfer characteristics in the tube bundle channels, which is crucial for the safe operation of the entire nuclear power plant system. Therefore, the numerical simulation research on the cross-mixing characteristics of fluids in inclined non-uniform heating tube bundle channels was conducted, and the influence of inclination and its coupling effect with non-uniform heating on fluid cross-mixing was analyzed in this paper. The results indicate that the inclined effect leads to fluid cross-mixing from bottom to top between rods, and forms vortex when encountering the upper heating rod, and the vortex intensity increases with the increase of the inclined angle. The low-temperature zone often arises on the lower surface of the heating rod and the high-temperature zone typically forms on its upper surface as a result of lateral fluid cross-mixing. Under the inclined and non-uniform heating conditions, when the high-power side is above, the effect of inclined and non-uniform heating on the fluid cross-mixing shows a competitive relationship between the rod and the channel wall. The vortex only occurs when the inclined effect is larger than that of the non-uniform heating. On the contrary, non-uniform heating dominates the transverse fluid cross-mixing. When the high-power side is located below, there is a synergistic effect of inclined and non-uniform heating on the fluid cross-mixing between the rod and the channel wall, promoting the generation of vortex. However, the natural convection effect from hot bottom to cold top is opposite to the above effect, which weakens the vortex intensity. The fluid cross-mixing direction between rods is determined only by the inclined direction.