In this study, a digital mask-based STED lithography technique was proposed, and the effective resolution of the proposed system was calculated analytically. The proposed STED lithography system uses two spatial light modulators to modulate the phase of an excitation beam and a depletion beam, respectively. The excitation spatial light modulator acts as a digital mask to form the patterning image, while the depletion spatial light modulator creates an image surrounding the projected excitation image. Thus, photopolymerization is suppressed by stimulated emission occurring in the depletion focus region surrounding the excitation focus, thereby improving lithographic resolution. Electromagnetic field and intensity distribution were calculated, and the resolution of the proposed STED lithography was simulated based on vectorial diffraction theory. An effective resolution of 72 nm was calculated under the condition of I_s 0.1, which is similar to the resolution of conventional STED lithography at 70 nm. These results analytically confirmed that the proposed STED lithography system could pattern a two-dimensional region simultaneously without the loss of resolution compared to conventional STED lithography.