It is desirable to fabricate materials with adjustable physical properties that can be used in different industrial applications. Since the property of a material is highly dependent on its inner structure, the understanding of structure–property correlation is critical to the design of engineering materials. 3D printing appears as a mature method to effectively produce micro-structured materials. In this work, we created different stainless-steel microstructures by adjusting the speed of 3D printing and studied the relationship between thermal property and printing speed. Our microstructure study demonstrates that highly porous structures appear at higher speeds, and there is a nearly linear relationship between porosity and printing speed. The thermal conductivity of samples fabricated by different printing speeds is characterized. Then, the correlation between porosity, thermal conductivity, and scanning speed is established. Based on this correlation, the thermal conductivity of a sample can be predicted from its printing speed. We fabricated a new sample at a different speed, and the thermal conductivity measurement agrees well with the value predicted from the correlation. To explore thermal transport physics, the effects of pore structure and temperature on the thermal performance of the printed block are also studied. Our work demonstrates that the combination of the 3D printing technique and the printing speed control can regulate the thermophysical properties of materials.