Plate anchors are of vital importance for both onshore and offshore facilities. The current study has been focused on the pullout capacity factors of rectangular anchors with wide range of aspect ratios under coupling effects of embedment ratios, anchor inclinations, overburden pressure and non-homogeneity of the clay. Three-dimensional small strain finite element (FE) analyses based on ABAQUS are carried out. After verifying the current model with the existing numerical solutions, the FE results are obtained, and relative comprehensive formulas have been proposed to evaluate the pullout capacity factor with the given parameters. The anchor with aspect ratio less than one has outlier performance in normally consolidated (NC) clay, which has also been discussed based on the soil flow mechanism.