Abstract: Tube and fin heat exchangers are widely utilized in industrial applications due to their straightforward construction and cost-effectiveness. Typically, enhancements in heat transfer performance are accompanied by an increase in resistance loss. Hence, it is crucial to enhance heat transfer while simultaneously reducing flow resistance, which is essential for optimizing heat exchanger design. At present, the research on the combination of splitter plate and tube bundle mainly focuses on the cross-flow tube bundle heat exchanger, and the research on the heat exchanger for the combination of splitter plate and tube-fin heat exchanger is not yet sufficient. Meanwhile, when the fin spacing changes, there are fewer studies on the effect of fin spacing on the comprehensive performance of manifold in tube-fin heat exchanger with splitter plate. Therefore, in this paper, the effect of splitter plate on the flow and heat transfer characteristics of heat exchangers with different fin spacing is investigated numerically. The findings indicate that the addition of splitter plates behind the circular tube can increase the heat transfer area, thereby enhancing the heat transfer capacity within the heat exchanger channel. Additionally, it makes the fluid flow more uniform and stable, effectively reducing flow resistance, and significantly improving the integrated enhanced heat transfer evaluation factor. Within the studied range of Reynolds number, when the fin pitch is 30 mm and the splitter plate length is 1.5 times the tube diameter, the heat exchange capacity in the heat exchanger channel is maximized, showing a 17.1% increase compared to the round tube alone. The resistance coefficient is reduced by 7.4%, while the comprehensive enhanced heat transfer evaluation factor is improved by 19.8%. Consequently, the addition of splitter plates not only increases the heat transfer area but also streamlines the channel fluid flow, effectively enhancing the heat exchanger's overall heat transfer capacity and offering extensive application potential in actual industrial production.