Abstract: Two-dimensional and three-dimensional finite element calculations of stress intensity factors for standard compact tension(CT) specimens were compared and analyzed. And a new calculation formula of stress intensity factors for standard CT specimens was established based on the three-dimensional finite element virtual crack closure method and verified using displacement extrapolation method of ANSYS. The results show that great differences existed between the stress intensity factors from calculation formula based on the two-dimensional analysis and those of actual three-dimensional CT specimens. Under the certain equivalent distributed force on the load-hole, the stress intensity factors at the most crack front regions were similar to those at the center of the CT specimen and were independent of the thickness. The fitting calculation formula of stress intensity factors at the crack front center of three-dimensional CT specimens was of high precision. And the relative errors between the fitting calculation values and the results of the displacement extrapolation method of ANSYS were less than 0.5%.