This study focuses on the basic relationships between nanohardness, residual stress, and micro/nanostructure of precision machined surfaces of high carbon steels. A series of nanoindentation tests were conducted on the cross-sections of the precision machined surfaces with ultrafine-grains or nanostructures. It was found that the nanostructured white layer significantly increases nanohardness, while the ultrafine-grained layer only slightly increases surface hardness. Residual stress affects the load-displacement curve shape at the onset of material yielding. Nanostructure makes a significant difference on the characteristics of a load-displacement curve, while ultrafine-grained structure exerts a slight influence. The influence of residual stress on the load-displacement curve can be estimated by finite element simulation of a nanoindentation. The simulation sensitivity analysis shows that the load-displacement curves are significantly affected by residual stress.