Abstract: Aiming at the large dispersion of waterhammer impact fatigue life and the lack of systematic quantitative research on the fatigue effect of weld geometric deviations for thinwalled enamelcoated inner tanks, this paper takes the straightweld and circumferentialweld joints of enamelcoated inner tanks as the research objects. Combining failure characterization, finiteelement simulation and DOE forming tests, the influences of typical geometric deviations including butt angle, incompletepenetration depth, assembly gap and flaringlap depth on weld stress distribution and fatigue performance are systematically analyzed, and the differentiated failure mechanisms of the two types of welds are revealed. The results show that the straight weld exhibits remarkably higher stress sensitivity to geometric deviations than the circumferential weld. When the incompletepenetration depth increases from −0.5 mm to −1.5 mm, the peak stress rises by 211.6 %; when the butt angle decreases from 175° to 160°, the stress increases by 50.7 %. These two parameters serve as the core control factors for fatigue failure of straight welds. For the circumferential weld, the stress increment induced by various geometric deviations is lower than 5 %. Its fatigue failure originates from the inherent stepinduced stress concentration of the lap structure, while geometric deviations only exert a secondary amplifying effect. The hierarchical geometricdeviation control scheme established via sensitivity analysis has been verified by trial production. It can increase the average waterhammer impact fatigue life of inner tanks by 30 % and effectively reduce test dispersion. This work provides references for reliability design and process control of similar thinwalled pressurebearing enamelcoated components.