The microscopic residual stresses beneath scratches on thermally treated (TT) UNS N06690 have been measured using synchrotron radiation x-ray diffraction; the effect of these residual stresses on initiating stress corrosion cracking (SCC) has been studied in 10% sodium hydroxide (NaOH) + 10 g/L lead oxide (PbO) solution at 330°C. Results show that scratching causes local residual tensile stresses parallel to the scratching direction at the scratched surface and local residual compressive stress normal to the scratching direction beneath the scratch. The residual tensile stresses at the scratched surface will act as a precursor of SCC. The residual compressive stresses beneath the scratch cannot stop crack growth of N06690 TT in 10% NaOH + 10 g/L PbO solution at 330°C.