A light intensity modulation method implemented by using a mask (101) includes the steps of: 1) based on a circle of confusion (CoC) function of an illumination system (102), an initial light intensity distribution of an illumination field of view (FOV) and a target light intensity distribution of the illumination FOV, calculating a transmittance distribution of the mask (101) used to modulate the initial light intensity distribution into the target light intensity distribution; 2) meshing the mask (101) according to a desired accuracy of the target light intensity distribution and determining a distribution of opaque dots in each of cells resulting from the meshing based on the transmittance distribution of the mask (101) and a desired accuracy of the transmittance distribution; and 3) fabricating the mask (101) based on the determined distribution of the opaque dots and then deploying the mask (101) in the illumination system. Advantages including a high modulation accuracy, an applicability to wide FOV size, light intensity and wavelength ranges and compatibility with established manufacturing processes can be attained.