The impact of inclined loading on bearing capacity of suction caissons over sand foundation is investigated by establishing an ideal elasto-plastic constitutive model which takes the rotation of principal stress direction into consideration. Through numerical integration, the variation in principal stress direction during shear deformation is obtained, and moreover, the influence of inclination angle of load on distribution of equivalent plastic strain is examined. Research result unveils that under inclined loading, equivalent plastic strain concentrates in the peripheral of caisson wall and the lower part of caisson. Soils inside the caisson are at elastic deformation state. In addition, the inclination angle of load has little influence on the relation between vertical load and settlement, but has evident impact on the relation between horizontal load and displacement. In the initial stage of deformation, the principal stress direction rotates apparently, and the rotation angle becomes larger with the increasing of load’s inclination angle. When vertical displacement ranges between 0.05D-0.10D, the principal stress direction reaches stable stage and stops rotating.