Abstract: Objective The purpose was to analyze distribution of work hardening at fusion line of welded joints at safe end of nuclear power one-water circuit, and to provide an analytical basis for distribution of mechanical properties of crack tip and driving force of crack extension. Methods Relationship between Vickers hardness and yield strength of 316L stainless steel under different work hardening degrees was obtained by experiments. The yield strength of fusion line attachment material of welded joints was obtained by non-uniform hardening law of welded joints. On this basis, the distribution of mechanical properties at crack tip on the fusion line were obtained by finite element simulation. Results The results showed that Vickers hardness was different on both sides of fusion line of welded joints, and material showed different degrees of work hardening, the Vickers hardness gradually decreases along both sides of the fusion line. Uneven work hardening law of welded joints could affect Mises stress, opening stress, equivalent plastic strain and opening strain of crack tip. Work hardening could increase the Mises stress and opening stress at the crack tip, and make the Mises stress and opening stress incline to the metal with higher work hardening degree. However, work hardening could inhibit the equivalent plastic strain and crack opening strain, the equivalent plastic strain and opening strain were biased towards the metal with lower degree of work hardening. Work hardening also affected stress triaxiality of crack tip, and increased crack tip strain rate and crack growth rate. Conclusion The work hardening of materials near fusion line of welded joints increased driving force of crack growth, accelerated the crack growth rate of defective cracks, and exacerbated failure of welded joints.