For the problems of sample deformation and burr enlargement due to large gap caused by wear in the stamping production process, the causes and related factors of tensile stress in the stamping shear process were explored through force analysis, and the theoretical derivation and experimental verification were carried out. The result shows that the average axial tensile stress P of specimen is proportional to sample width W, central layer inward movement coefficient  χ, material property correlation coefficient K1 and difference between the relative clearances in shear test and maximum shear stress state(R-R2), and it is inversely proportional to the die edge size Dd. When the shear force is in a non-maximum shear stress state, the specimen generates a bending moment during the shear process, which causes the central layer of specimen to move inward. However, the compressive stress endured by the material inside the central layer is not symmetrical to the tensile stress endured by the material outside the central layer, and the tensile stress of material is greater than the compressive stress, making the entire sample in a tensile stress state.