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Calculation models were established based on the elastic fracture theory and complex function theory for the surface oblique crack on round tube. Change in stress intensity factors and critical crack length were investigated when surface oblique crack on round tube developing propagation considering different influencing factors. Take crack typeⅠ and typeⅡ for example, by using the strain energy density theory, a complete analysis was performed. The influence of crack initiation angle, crack angle and size on the stress intensity factors was calculated. The influence curves of crack angle on two stress intensity factors of the mixed-mode crack were obtained. Then, the influence extent was compared. Moreover, the complete analysis on the influence which cracked initiation angle, crack angle on the critical crack length was performed. The results showed that with the increase of the crack angle, the maximal and minimal values of the two stress intensity factors (KⅠ,KⅡ) were same, however, the tendency was opposite. Moreover, to typeⅠ crack , the stress intensity factors on the position of β=0 and β=2π were equal to zero.