Abstract: Thermal behavior and heat transfer characteristics of a composite sandwich structures with lattice cores under loading with a constant temperature field were simulated by computational fluid dynamics FLUENT software during forced convection with auxiliary fluid. The distribution and characteristics of flow field, such as the fields of pressure, velocity and temperature, were analyzed. The influence of structural morphology on the inner end-wall and heat transfer patterns in a unit cell was described in details. Three dimensionless parameters Reynolds number, Nusselt number and pressure drop coefficient, scaling by the characteristic length of unit cell were used to characterize and assess the heat transfer performance of structure. Furthermore, by introducing concepts of the minimum permeability, maximum permeability and horizontal permeability of temperature, the heat transfer performance of structure was visually characterized. The analytic results indicate that heat transfer performance of this lattice-cores sandwich structure can be evidently improved in the case of forced convection, and therefore reveal the structure is more suitable for the mulitifunctionalities of lightweight structure achievement in the future.