Residual stresses levels and their distributions in thin films have an important effect on their mechanical properties. The non-destructive analysis by pseudo-grazing incidence X-ray diffraction (GIXRD) allows us to define residual stresses gradients as a function of thin film depth. In case of pseudo-GXRD, we must take into account the effects due to surface roughness on residual stress analysis. We have investigated firstly a set of carbon steel specimens with different surface roughness (RZ varies from 4.2µm to 9.5µm) obtained by grinding. All specimens were tempered to eliminate the residual stresses due to machining. With K radiation of Chromium, Bragg peak positions were determined with various incidence angles (varies from 1° to 78°) for each specimen. Secondly, a carbon steel specimen containing 4 zones with different surface roughness was loaded elastically in tension, pseudo-GIXRD has used for stress analysis on the loaded specimen with various incidence angles. The peak shifts due to the surface roughness were studied as function of different roughness and different incidence angles. The stress relaxation due to surface roughness was then studied.