Abstract: To address the challenges in predicting ductile fracture of 3Cr13MoV martensitic stainless steel under complex loading conditions, the fracture mechanisms were systematically investigated through mechanically testing under multi-axial stress states and microscopic damage evolution analysis. Based on the evolutionary processes of voids, a novel uncoupled ductile fracture prediction model was proposed. This model introduced maximum shear stress and maximum principal stress as damage evolution correction factors and quantitatively revealed the induction mechanism of maximum principal stress on void coalescence under stress triaxiality control. Finite element simulations and experimental validation showed that the model accurately predicts behavior across various stress levels.