Abstract: This study aims to investigate the impact of sample structure on surface roughness in Selective Laser Melting (SLM) processes and to establish a theoretical model for predicting surface roughness. A mathematical model is constructed based on the relationship between the angle and radius of internal holes and their roughness, analyzing the surface morphology of formed parts under different parameters and exploring the influence of various parameters on surface roughness. Key factors affecting the surface roughness of samples are analyzed, including the stair-stepping effect, powder adhesion, and warpage deformation, all of which can influence surface roughness. A predictive model linking the formed structure with surface roughness is established. Experimental results show that different angles and hole diameters significantly affect the surface roughness of samples. When the printing angle of the hole exceeds 50°, the roughness value of the inner surface of the hole begins to increase sharply. For instance, at a 4 mm hole diameter and a 50° angle, the roughness is 7.01 μm; this increases to 24.53 μm at a 70° angle. As the angle and hole diameter increase, these factors collectively impact the surface quality of the samples. Through the construction of the mathematical model, it was found that roughness prediction is effective at medium to low angles, but noticeable errors occur when the printing angle increases to 80°. The model allows for appropriately accurate predictions of surface roughness using parameters, providing a solid theoretical basis and technical support for optimizing surface quality.