This study describes a design framework of miniaturized heat exchangers with forced convection heat transfer by applying a flow and thermal resistance network analysis (coupled analysis). As the test cooling jacket, a thin heat exchanger that straight fin allays is mounted inside the cooling jacket, and an aspect ratio of the cross-sectional area in the cooling jacket was 1:17, was prepared. The working fluid was air. The coupled network model in the cooling jacket was developed using the obtained performance data. The proposed coupled network model can predict the temperature distribution of the cooling air in the jacket from the enthalpy conservation between each element. In addition, the local heat transfer performance and flow rate distribution that affect the heat exchange performance were represented by the experimental and analytical results. Finally, the design optimization was applied by the conducted coupled network model. The research proposed the construction method of the first-order optimization scheme of the thermal design for the miniaturized heat exchangers based on the coupled network model.