Selective laser melting (SLM) technology has great advantages in processing hollow thin-walled structures. Hollow thin-walled structures with equal stiffness are calculated and designed by stiffness theory, and the correctness of the design is verified by the combination of experiment and numerical simulation. The results show that under bending load, the deformation area is mainly concentrated near the center line of the maximum bending moment. Under the same force, the displacement of the three kinds of hollow rectangular section thin-walled structural parts is almost the same. For single thin-walled structural parts, because the elastic modulus is lower than that of solid block parts, the displacement produced by its center is smaller than that of hollow rectangular section thin-walled structural parts. The bending process of the finite element model of thin-walled structure is simulated, and the simulated results of equivalent stress and strain are consistent with the experimental results. The research conclusion can provide theoretical support for the section design of thin-walled structures processed by SLM.