The minimum characteristic size for 316L stainless steel was determined using a laser powder bed melting experiment of the lattice structure. Four types of lattice cell structures were designed. The relationship between different lattice cell configurations, packed density, and heat exchange efficiency was simulated by Materiallise Magics software. A lattice cell configuration with a better heat exchange efficiency was selected. Three different densities with the best lattice cell configuration were filled, and Materiallise Magics software calculated the heat exchange area of the three different densities of lattice structures. Laser powder bed melting additive manufacturing under three densities was used to fabricate a 316L stainless steel lattice structure. Computed tomography was used to reconstruct the three-dimensional image of the lattice structure, and the heat exchange area of the structure was determined. The heat exchange efficiency value was predicted using a mathematical model, and the measured value was calculated and compared. The difference between the mathematical model predicted and measured values of heat exchange efficiency of 316L stainless steel value is about 11%.