Semi- elliptic surface crack is a common defect in metal structures,which is easy to propagate under the effects of external factors and may even result in the damage of the structures.The service life of the damaged struc-tures can be greatly extended by using the fiber- reinforced polymer (FRP) to strengthen and repair them.In this paper,the finite element software Abaqus is employed to numerically analyze the stress intensity factor (SIF) of the semi- elliptic surface crack in the X80 steel plate strengthened with FRP under tensile load,and the semi- empirical expression of the SIF is obtained.The results show that,under the uniform tensile load,the crack shape ratio has a greater effect on the SIF as well as on the reinforcement effect,and the relative crack depth also affects them to a certain degree.