Traditional three-dimensional (3D) vector imaging models treat the electric field distribution in the entrance pupil of projector by transforming the distribution in the local coordinate or ignoring the axial component of the mask diffraction spectrum (MDS). The accuracy of the model with the latter should be discussed in immersion lithography. The traditional 3D vector imaging model and a modified 3D lithography imaging model which integrates all the vector effects of plane wave through the whole imaging system are introduced. Then the influence of the axial component of MDS on the lithography imaging performance is analyzed by the modified imaging model and the resist model of commercial software PROLITHTM. The results are discussed by using frequency spectrum analysis. The simulation results show that the accuracy of traditional 3D vector imaging model is degraded in hyper numerical aperture (NA) system for the axial component of MDS on the entrance pupil of projector cannot be ignored any more in immersion lithography. This demonstrates that only the modified 3D imaging model under partially coherent illumination condition can satisfy the requirement of hyper NA lithography simulation.