The work aims to explore the effect of three-dimensional surface roughness Sa on the bending fatigue life of 18CrNiMo7-6 steel under the fixed load. 18CrNiMo7-6 steel rotating bending fatigue specimens with different surface roughness and texture path were prepared by sandpaper grinding. The surface roughness parameters Sa and three-dimensional surface topography parameters Sq, Sz, Ssk, and Sku of all specimens were measured. Rotational bending fatigue test was carried out on the specimen to analyze the fatigue life of the specimen. The fatigue life of axial textured specimens with the same or similar roughness was greater than that of circumferential textured specimens. Under the same texture direction, the lower the three- dimensional surface roughness was, the higher the fatigue life was. The fatigue life times of specimens were significantly correlated with Sa and Sq, Sz, Ssk, and Sku. For 18CrNiMo7-6 steel rotating bending fatigue specimens, machining grooves perpendicular to fatigue stress are more harmful than machining grooves parallel to fatigue stress. Reducing the surface roughness of the 18CrNiMo7-6 steel specimen can effectively improve the rotational bending fatigue life of the specimen. The surface skewness Ssk of the specimen with texture direction parallel to the fatigue stress direction has no obvious influence on the fatigue life of the part.