Abstract: Objective A series of experiments are carried out by designing the test specimen of TA23 titanium alloy sheet base metal and three kinds of welded joints (butt, T-type and cross-type), the aim is to obtain the nominal stress S-N curve and obtain the fatigue strength of each welded joints. Methods The microstructure length of TA23 titanium alloy welded joints is determined by the experiment data and the Neuber stress average method, which can be used for the calculation of effective stress and virtual notch radius.The virtual notch radius can be used as the reference radius of TA23 titanium alloy welded joints. Considering the influence of virtual radius, a finite element model is established to obtain the stress gradient at the notch of various typical welded joints. Results The notch effective stress is calculated based on the experimental data and stress gradient by using the Neuber stress average method, the dispersion band index is defined, and the curve of the dispersion band index of the S-N curve changes with the length of the microstructure is obtained. The results show that the dispersion band index is the smallest when the length of the microstructure is 0.08 mm. Conclusion The virtual notch radius based on the microstructure length can provide a reference for the notch stress evaluation of titanium alloy sheet welding structures.