The strong axial electric field component can be obtained in the focus area by an annular diaphragm with a larger radius. In contrast, by another annular diaphragm with a smaller radius which combines with a π phase plate, the axial electric field distribution can be obtained in the focus area with the vibration direction opposite to that of the axial electric field produced by the annular diaphragm with a larger radius. Consequently, the focused spot formed by the annular diaphragm with a larger radius in the focus area is reshaped. In certain conditions, the size of the focused spot can be greatly reduced. The study results show that, compared with that when using sing annular diaphragm, the size reduction of the focused spot with the proposed method can be more than 40 nm.