Abstract: Gravity anchor, serving to offshore mooring systems, is suitable for offshore shallow waters. Due to its advantages of simple and convenient construction and low maintenance cost, it is preferable in the field of offshore engineering. In the current design specifications, a semi-analytical and semi-empirical method is used for estimating the holding capacity of gravity anchor in the single layer soils and for the complex layered soils the finite element method is recommended to be used for checking. For the geological conditions of actual stratified soils at a floating photovoltaic site, the bearing mechanism of rectangular gravity anchors under actions of dragging load and dead weight is studied by using the finite element analysis, and the load bearing properties in the spaces of vertical-horizontal, vertical-bending moment and horizontal-bending moment loads are quantitatively analyzed respectively by using the method of failure envelope surface of bearing capacity. Through specific design cases, it is explained how to use the obtained failure envelopes of bearing capacity for carrying out checking, in which the mooring point position and dragging angle are take into acount. The results indicate that under the case of layered soils, there is significant coupling between the combined loads on the gravity anchor and the changing tendency of the bearing capacity exhibits different characteristics under the failure modes dominated by different loads. The method for calculating the bearing capacity of the gravity anchor proposed in the study can provide technical support for the design and optimization of offshore mooring anchor foundation.