Abstract: A numerical study on fluid flow characteristics and heat transfer performance of composite lattice truss core sandwich structure with a constant localized internal heat source was presented. The thermal resistance network and the non-dimensional parameters measured by the channel height were respectively adopted to analysis and characterize the thermal field of heat source and active cooling performance. The effects of inclination angle on fluid flow and temperature of heat source were explored. An optimization analysis of thermo-mechanical performance was carried out based on the relationship between inclination angle and the maximum temperature of heat source. The results suggest that this composite sandwich structure has excellent active cooling performance, and with an increase of inclination angle, the heat transfer efficiency is improved, leading to a reduction of structural maximum temperature.