A method for improving lateral resolution and reducing imaging distortion of optical subtraction microscopy is pro-posed. First, an azimuthally polarized (AP) light is modulated by an annular aperture. Then, an image with higher lat-eral resolution is obtained by subtracting an image obtained by an annular AP beam from an image obtained by a ra-dially polarized beam. The simulation results demonstrate that compared with the case without the annular aperture, negative side-lobes in the effective point spread function are effectively suppressed, and the imaging quality of sub-traction microscopy is obviously enhanced.