Pure titanium is often used in the manufacture of pressure vessels due to its excellent corrosion resistance. Pressure vessels are generally operated in various corrosive media and subjected to varying degrees of corrosion. Stress corrosion cracking is one of the most dangerous forms of damage to pressure vessels used in various fields. Welded joints become the weak link of the pressure vessels because of the uneven microstructure and welding residual stress, which could cause stress corrosion and directly affect the overall performance and service life of pressure vessels. At present, as a method to improve the mechanical and corrosion properties of materials, shot peening has been widely studied. However, shot peening often leads to the increase of surface roughness and even causes defects such as cracks and surface damage, which will affect the effect of improving the corrosion resistance of materials. It remains to be further studied that the specific influence of surface roughness on the stress corrosion resistance of metal materials. In this work, the stress corrosion behavior of the original samples, ultrasonic shot peening (USSP) samples and USSP with surface polished samples of TA2 titanium welded joints in 10%HCl solution were studied by slow strain rate tension (SSRT) experiment. OM, TEM and SEM were used to observe the microstructure and corrosion fracture morphology of the welded joints. The surface roughness and residual stress of different processed samples were measured, and the corrosion mechanisms were analyzed. The results showed that both stress corrosion and hydrogen embrittlement occurred in pure titanium welded joints in this system, and weld metal (WM) was the weakest link in the welded joint. The stress corrosion cracking susceptibility index (I_SCC) of the original sample in this system was 25.61%, indicating a tendency of stress corrosion. The I_SCC of the USSP sample was reduced by 28.78%, and that of the USSP with surface polished (1500#) sample was reduced by 53.3%; both of them had no obvious tendency of stress corrosion in the system. The roughness of the USSP surface could cause stress concentration to form a crack source, which was similar to the pitting propagation. USSP with surface polished treatment reduced the surface roughness, achieving the homogenization of the stress distribution and increasing the elongation and the plasticity of the samples, which could further improve the stress corrosion cracking resistance.